<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/59871>59871</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang adds `/usr/include` to header search path while cross compiling with mingw-w64
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          godvino
      </td>
    </tr>
</table>

<pre>
    Trying to cross compile to windows using clang and mingw-w64 results in clang adding `/usr/include` to its header search path. This breaks compiling some projects that check for the presence of certain headers like `alloca.h` because it then uses the `alloca.h` from the host system which causes errors.

```
 ❯ clang --target=x86_64-w64-mingw32ucrt main.c -o main -v
clang version 15.0.6 (Fedora 15.0.6-3.fc37)
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: /usr/bin
 "/usr/bin/clang-15" -cc1 -triple x86_64-w64-windows-gnu -emit-obj -mrelax-all --mrelax-relocations -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name main.c -mrelocation-model pic -pic-level 2 -mframe-pointer=none -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -mms-bitfields -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -mllvm -treat-scalable-fixed-error-as-warning -debugger-tuning=gdb -v -fcoverage-compilation-dir=/var/home/godvino/Documents -resource-dir /usr/lib64/clang/15.0.6 -internal-isystem /usr/lib64/clang/15.0.6/include -internal-isystem /usr/x86_64-w64-mingw32ucrt/sys-root/mingw/include -internal-isystem /usr/x86_64-w64-mingw32ucrt/sys-root/mingw/usr/include -internal-isystem /usr/include -fdebug-compilation-dir=/var/home/godvino/Documents -ferror-limit 19 -fno-use-cxa-atexit -fgnuc-version=4.2.1 -exception-model=seh -fcolor-diagnostics -faddrsig -o /tmp/main-50542d.o -x c main.c
clang -cc1 version 15.0.6 based upon LLVM 15.0.6 default target x86_64-redhat-linux-gnu
ignoring nonexistent directory "/usr/x86_64-w64-mingw32ucrt/sys-root/mingw/usr/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib64/clang/15.0.6/include
 /usr/x86_64-w64-mingw32ucrt/sys-root/mingw/include
 /usr/include
End of search list.
 "/usr/bin/x86_64-w64-mingw32ucrt-ld" -m i386pep -Bdynamic -o main.exe /usr/x86_64-w64-mingw32ucrt/sys-root/mingw/lib/crt2.o /usr/lib/gcc/x86_64-w64-mingw32ucrt/12.2.1/crtbegin.o -L/usr/lib/gcc/x86_64-w64-mingw32ucrt/12.2.1 -L/usr/x86_64-w64-mingw32ucrt/sys-root/mingw/lib -L/usr/x86_64-w64-mingw32ucrt/sys-root/mingw/mingw/lib -L/usr/lib /tmp/main-50542d.o -lmingw32 -lgcc -lgcc_eh -lmoldname -lmingwex -lmsvcrt -ladvapi32 -lshell32 -luser32 -lkernel32 -lmingw32 -lgcc -lgcc_eh -lmoldname -lmingwex -lmsvcrt -lkernel32 /usr/lib/gcc/x86_64-w64-mingw32ucrt/12.2.1/crtend.o```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJysVkFv4zoO_jXOhaBhy4nTHHLobCbAArO3wV4HskTbmsqSIcpp-u8Xcpxm2pl23wseUKQyRX6iyI8UJbPpHNE-23zJNoeVnGLvw77z-mScXzVev-y_hxfjOogeVPDMoPwwGktJ8Gyc9s8MEycNZaXrQDoNg3HdMz7XawjEk40Mxl23tU66WV1k4jhxyMTROGUnTVldJEwTGXqSmgIwyaB6GGXsc_jeG4YmkHy6upBw2A8EY_A_SUWG2MsIqif1BK0PEPu0R0xOEfgWFIUojVvgGax5ouSJtNYrmffJg4aUnJjAxGTuYGLiGeidXhv8MMt7zxH4hSMN8Nwb1cMMwEAh-MB5Vhyy4nH5rYvlb_6E7KvIdofs8bgEBzHK0FHMqsP5of5Rr1MMcY5mJSYVIgzSuFwB-nkFeLogXcxPFNh4B-UmL_IaMvFwJO2DXARY5a2qtpnYXYy-L2c9wi-HLSnFzk2LVh9Iahi8Jpt0R8_mfNn6t-MorSV9MCFtvWa0Me56QyHeSMVxdhXLTSYEoFIlYAxmtPSBE4A0mIi--Qk4BLLyjNJawOtHoJSTaLxjQG1YNpawDUSAypIMKDliQ60PhI1UT-T0Tc_a04AnCqY1FGaxkkHjSdqJ0MmBGDDFGVtjL4LXBAy3g3GODYxGAY5GoaUTWRCAQxvkQDh64yKFrDo47wiwHWTskUJwHrBtR1TexSBVSrt3gK3zGPzkUqFg0gUclHccw6SiDyitkTy7NjA2JraGrGbAdnIpcBjT3TirDgIWPqEapxRfrNeAcXI0CzpyFJLTQ4pDygPJiKykvQTRnEnjzGKUjM8yuFRxqKmZuo5CAjKuy6pDpxvAE2Cr_ImC7AgvBXqJjk7kOGTieJKJBb0fKBPHpcVk4njwahrIRQYMxH4KipLNjU3WNPX6ypxMHBd64xxVJy2apfz-j8Wt1Xxm--fCy8SRXxiD92k5b_zzcG_a4WegryrtnIx7w91ekmvNYCKUuwvzJiZUZ4ky0tlEwLZzk8KltWTVYZ2LvASks6Lxxv6sOjD1MwWsD6iN7JznaFQ6Rmod2HSpa2XiGIcx3TmV1abYrIXOPeAZ1FJavza0uT-862qNZNIwjd7Bt2___c9VrKmVk41wIfy1mQTSvYxojZvOt5ZmOudD4nKqx7PhSC6CNoFSeb286Vl3py-BXHq-qK7pyoTI8zw1vuVl4yjD_NwFyqrH3_WrfyX96utn-n-d9e_172D6e4g34q9Op1d28dUajvmHr8Cfz0ar52dhAFM91CONgF_0i5ODeX3ycjrTfVewpknBCVHk_k3QUnko9RlaKRLpL9YNdcYlyn67B-NXs7_p_L2mH0Ckz4-q0S6ggLZT6vL7I5W3HbzV8zu46NA5rfiUZhO0Up_kaGY77snaeTUxhXnxRMHRRXYn_ivC_ekjp3P_Ooet9L7Su2onV7Qv621VFmW5qVf9ftsURbErH7Yb2ejmoRbrelNUu1LuRL1ttvXK7EUhqqIstuW63JV1vqvLByU2u40qq2anKFsXNEhj8_S45j50K8M80X6ze9iWKysbsnwdu8N-nkSaqeNsXaTK4ZtZNNHS_nV65k9m59_n5jSSWnozuafG92xif5vSV1Ow-z7GkVNXEccUURP7qcmVH1KQ7en6D5dZOx2drsOZOM43-l8AAAD__3cFBX8">