$ nix build -f . swiftPackages.cxx-interop-test --log-format multiline -L
swift-cxx-interop-test> Running phase: unpackPhase
swift-cxx-interop-test> unpacking source archive /nix/store/nf6dg34afc7p4mjxxkpgc6gs294a4jyb-src
swift-cxx-interop-test> source root is src
swift-cxx-interop-test> Unpacking SwiftPM dependencies
swift-cxx-interop-test> Running phase: patchPhase
swift-cxx-interop-test> Running phase: updateAutotoolsGnuConfigScriptsPhase
swift-cxx-interop-test> Running phase: configurePhase
swift-cxx-interop-test> no configure script, doing nothing
swift-cxx-interop-test> Running phase: buildPhase
swift-cxx-interop-test> SwiftPM flags: -j 16 -c release -Xswiftc -module-cache-path -Xswiftc /nix/var/nix/builds/nix-build-swift-cxx-interop-test.drv-0/b/module-cache -Xswiftc -I -Xswiftc /nix/store/im17i7wbpqrhfpvyh5czlsvjhp00ij4q-swift-testing-6.2.3-include/lib/swift/macosx/testing -Xswiftc -I -Xswiftc /nix/store/h2bri7l88h31bbjrsv8m38y2y8vqqpck-swift-stdlib-6.2.3-dev/lib/swift/macosx -Xswiftc -I -Xswiftc /nix/store/im17i7wbpqrhfpvyh5czlsvjhp00ij4q-swift-testing-6.2.3-include/lib/swift/macosx/testing -Xswiftc -I -Xswiftc /nix/store/h2bri7l88h31bbjrsv8m38y2y8vqqpck-swift-stdlib-6.2.3-dev/lib/swift/macosx
swift-cxx-interop-test> warning: /var/empty/Library/org.swift.swiftpm/configuration is not accessible or not writable, disabling user-level cache features.
swift-cxx-interop-test> warning: /var/empty/Library/org.swift.swiftpm/security is not accessible or not writable, disabling user-level cache features.
swift-cxx-interop-test> warning: 'src': Warning: supplying the --target arm64-apple-macosx14.0 != arm64-apple-darwin argument to a nix-wrapped compiler may not work correctly - cc-wrapper is currently not designed with multi-target compilers in mind. You may want to use an un-wrapped compiler instead.
swift-cxx-interop-test> Building for production...
swift-cxx-interop-test> [0/4] Write sources
swift-cxx-interop-test> [1/4] Write swift-version--41BD1BF3460DAC2D.txt
swift-cxx-interop-test> [3/5] Compiling CxxInteropTest SwiftStruct.swift
swift-cxx-interop-test> [3/5] Write Objects.LinkFileList
swift-cxx-interop-test> Warning: supplying the --target arm64-apple-macosx10.13 != arm64-apple-darwin argument to a nix-wrapped compiler may not work correctly - cc-wrapper is currently not designed with multi-target compilers in mind. You may want to use an un-wrapped compiler instead.
swift-cxx-interop-test> clang: warning: overriding '-mmacos-version-min=14.0' option with '--target=arm64-apple-macosx10.13' [-Woverriding-option]
swift-cxx-interop-test> [4/5] Linking CxxInteropTest
swift-cxx-interop-test> Build complete! (2.18s)
swift-cxx-interop-test> swiftc -parse-as-library -emit-clang-header-path Check-SwiftStruct.h -module-name Check -cxx-interoperability-mode=default Sources/SwiftStruct.swift -c -o SwiftStruct.o
swift-cxx-interop-test> clang++    -c -o main.o main.cpp
swift-cxx-interop-test> clang++ main.o SwiftStruct.o -o SwiftToCxxInteropTest
swift-cxx-interop-test> ld: warning: object file (SwiftStruct.o) was built for newer macOS version (26.0) than being linked (14.0)
swift-cxx-interop-test> Running phase: installPhase
swift-cxx-interop-test> warning: /var/empty/Library/org.swift.swiftpm/configuration is not accessible or not writable, disabling user-level cache features.
swift-cxx-interop-test> warning: /var/empty/Library/org.swift.swiftpm/security is not accessible or not writable, disabling user-level cache features.
swift-cxx-interop-test> warning: 'src': Warning: supplying the --target arm64-apple-macosx14.0 != arm64-apple-darwin argument to a nix-wrapped compiler may not work correctly - cc-wrapper is currently not designed with multi-target compilers in mind. You may want to use an un-wrapped compiler instead.
swift-cxx-interop-test> warning: /var/empty/Library/org.swift.swiftpm/configuration is not accessible or not writable, disabling user-level cache features.
swift-cxx-interop-test> warning: /var/empty/Library/org.swift.swiftpm/security is not accessible or not writable, disabling user-level cache features.
swift-cxx-interop-test> Running phase: fixupPhase
swift-cxx-interop-test> checking for references to /nix/var/nix/builds/nix-build-swift-cxx-interop-test.drv-0/b/ in /nix/store/ncir3cf7mcgcs399189bh8i31w6n7m9j-swift-cxx-interop-test...
swift-cxx-interop-test> patching script interpreter paths in /nix/store/ncir3cf7mcgcs399189bh8i31w6n7m9j-swift-cxx-interop-test
swift-cxx-interop-test> stripping (with command strip and flags -S) in  /nix/store/ncir3cf7mcgcs399189bh8i31w6n7m9j-swift-cxx-interop-test/bin
swift-cxx-interop-test> Running phase: installCheckPhase
swift-cxx-interop-test> Hello, Swift!
swift-cxx-interop-test> Hello, C++!

Does this patch fix the Linux build of Swift?

diff --git a/pkgs/development/compilers/swift/compiler/default.nix b/pkgs/development/compilers/swift/compiler/default.nix
index 5bb32d8496..e83cd984bb 100644
--- a/pkgs/development/compilers/swift/compiler/default.nix
+++ b/pkgs/development/compilers/swift/compiler/default.nix
@@ -148,7 +148,7 @@
       -e "s|${clang.cc}/bin/clang|$unwrappedClang|g" \
       -e "s|^\(\s*\)\($unwrappedClang\) \"@\\\$responseFile\"|\1argv0=\$0\n\1${bash}/bin/bash -c \"exec -a '\$argv0' \2 '@\$responseFile'\"|" \
     ${lib.optionalString (clang.libcxx != null) ''
-      -e 's|$NIX_CXXSTDLIB_COMPILE_${clang.suffixSalt}|-isystem '$SWIFT_BUILD_ROOT'/libcxx/include/c++/v1|g'
+      -e 's|$NIX_CXXSTDLIB_COMPILE_${clang.suffixSalt}|-cxx-isystem '$SWIFT_BUILD_ROOT'/libcxx/include/c++/v1|g'
     ''}
     chmod a+x "$targetFile"
   '';

Nope. Fails.

build/src/llvm-project/llvm/include/llvm/CAS/CASReference.h:12:2: note: in module 'LLVM_Utils' imported from /build/src/llvm-project/llvm/include/llvm/CAS/CASReference.h:12:
#include "llvm/ADT/ArrayRef.h"
 ^
/build/src/llvm-project/llvm/include/llvm/Support/type_traits.h:35:13: error: missing '#include <type_traits>'; 'is_class' must be defined before it is used
      !std::is_class<UnderlyingT>::value && // Filter conversion operators.
            ^
/build/src/llvm-project/llvm/include/llvm/ADT/Hashing.h:351:36: note: in instantiation of template class 'llvm::is_integral_or_enum<const void *>' requested here
  : std::integral_constant<bool, ((is_integral_or_enum<T>::value ||
                                   ^
/build/src/llvm-project/llvm/include/llvm/ADT/Hashing.h:368:18: note: in instantiation of template class 'llvm::hashing::detail::is_hashable_data<const void *>' requested here
std::enable_if_t<is_hashable_data<T>::value, T>
                 ^
/build/src/llvm-project/llvm/include/llvm/ADT/Hashing.h:560:63: note: while substituting deduced template arguments into function template 'get_hashable_data' [with T = const void *]
    buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg));
                                                              ^
/build/src/llvm-project/llvm/include/llvm/ADT/Hashing.h:608:17: note: in instantiation of function template specialization 'llvm::hashing::detail::hash_combine_recursive_helper::combine<const void *, const void *>' requested here
  return helper.combine(0, helper.buffer, helper.buffer + 64, args...);
                ^
/build/src/swift/include/swift/Basic/SourceLoc.h:291:12: note: in instantiation of function template specialization 'llvm::hash_combine<const void *, const void *>' requested here
    return hash_combine(Val.Start.getOpaquePointerValue(),
           ^
/nix/store/qarrb8yfby1yyypm32vabzgxgq3w41ma-gcc-15.2.0/include/c++/15.2.0/type_traits:654:12: note: definition here is not reachable
    struct is_class
           ^
/build/src/swift/SwiftCompilerSources/Sources/Basic/SourceLoc.swift:13:8: error: could not build C module 'BasicBridging'
import BasicBridging