Fix cross compilation of binding-generator

[AlexanderStein]

Pass -nostdlibinc to clang so that host path will not be included, as they will break compilation with target SDK toolchain:
=== Using OpenCV headers from: /opt/sdk/dev/sysroots/armv8a-tq-linux/usr/include/opencv4
=== Clang: clang version 22.1.8
=== Clang command line args: [
"-isystem/opt/sdk/dev/sysroots/x86_64-tqsdk-linux/usr/lib/clang/22/include",
"-isystem/usr/local/include",
"-isystem/usr/include",
[...]

Please also consider adding this as a fix to 0.99.1. Currently build breaks on master for systems with both openvc5 and opencv4 installed, but the project requiring opencv4.

[Copilot]

Pull request overview

This PR adjusts how the binding generator discovers Clang’s default C/C++ include search paths so cross-compilation header parsing won’t accidentally pick up host system include directories.

Changes:

• Pass -nostdlibinc to clang_sys::support::Clang::find(...) when collecting cpp_search_paths, to prevent host standard library include paths from being captured and later forwarded into the libclang parse.

---

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[twistedfall]

This breaks the CI unfortunately, with errors indicating being unable to include system headers, e.g.:

  ===    /Users/runner/work/opencv-rust/opencv-rust/src_cpp/ocvrs_common.hpp:4:10: fatal error: 'memory' file not found

[AlexanderStein]

I have no idea why the ubuntu 22.04 build breaks

[opencv 0.99.0] ===    /../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/cstdint:47:11: error: no member named 'int8_t' in the global namespace
[opencv 0.99.0] ===    /../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/cstdint:48:11: error: no member named 'int16_t' in the global namespace
[opencv 0.99.0] ===    /../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/cstdint:49:11: error: no member named 'int32_t' in the global namespace
[opencv 0.99.0] ===    /../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/cstdint:50:11: error: no member named 'int64_t' in the global namespace
[...]

As the include paths compared to ubuntu 24.04 are identical beside the version number, I suspect the LLVM-14 installation is somehow borked.
BTW: Why is clang-15 used with LLVM-14?

For Mac the include paths look good

  === Clang command line args: [
      "-isystem/Applications/Xcode_16.4.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/17/include",
      "-I/Users/runner/build/opencv/opencv-4.13.0-build",
      "-F/Users/runner/build/opencv/opencv-4.13.0-build",
      "-I/Users/runner/work/opencv-rust/opencv-rust/src_cpp",
      "-F/Users/runner/work/opencv-rust/opencv-rust/src_cpp",
      "-DOCVRS_PARSING_HEADERS",
      "-includeocvrs_common.hpp",
      "-std=c++17",
  ]

I don't have a Mac so I don't know where the memory header actually is located. How can we debug/proceed here?