<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/78721>78721</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc] unable to attempt fullbuild as a runtime library due to system headers
        </td>
    </tr>

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

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

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

<pre>
    My Vscode configuration for `cmake`:
```json
{
  "cmake.configureSettings": {
    "LLVM_ENABLE_RUNTIMES": [
      "libc",
      "compiler-rt"
    ],
    "LLVM_ENABLE_PROJECTS": [
      "clang",
      "lld"
    ],
    "LLVM_LIBC_FULL_BUILD": true,
    "CMAKE_EXPORT_COMPILE_COMMANDS": true,
    "LLVM_LIBC_INCLUDE_SCUDO": true,
    "LLVM_USE_LINKER": "lld",
    "CLANG_DEFAULT_LINKER": "lld",
    "CLANG_DEFAULT_RTLIB": "compiler-rt",
    "COMPILER_RT_BUILD_SCUDO_STANDALONE_WITH_LLVM_LIBC": true,
    "COMPILER_RT_BUILD_GWP_ASAN": false,
    "COMPILER_RT_SCUDO_STANDALONE_BUILD_SHARED": false,
    "CMAKE_CXX_COMPILER_LAUNCHER": "/usr/bin/sccache",
    "CMAKE_C_COMPILER_LAUNCHER": "/usr/bin/sccache"
  },
  "cmake.sourceDirectory": "${workspaceFolder}/llvm",
}
```
I cannot finish the fullbuild as the compiler somehow pulls in the system headers that undermine the libc's headers.

The compilation command is as the following:
```bash
/home/schrodingerzy/Documents/llvm/llvm-project/build/bin/clang++ --target=x86_64-unknown-linux-gnu -DLIBC_NAMESPACE=__llvm_libc_18_0_0_git -I/home/schrodingerzy/Documents/llvm/llvm-project/libc -isystem /home/schrodingerzy/Documents/llvm/llvm-project/build/runtimes/runtimes-bins/libc/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O2 -g -DNDEBUG -std=gnu++17 -fpie -ffreestanding -fno-builtin -fno-exceptions -fno-lax-vector-conversions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -Wall -Wextra -Werror -Wconversion -Wno-sign-conversion -Wimplicit-fallthrough -Wwrite-strings -Wextra-semi -Wnewline-eof -Wnonportable-system-include-path -Wstrict-prototypes -Wthread-safety -Wglobal-constructors -DLIBC_COPT_PUBLIC_PACKAGING -MD -MT libc/src/sched/linux/CMakeFiles/libc.src.sched.linux.sched_rr_get_interval.dir/sched_rr_get_interval.cpp.o -MF libc/src/sched/linux/CMakeFiles/libc.src.sched.linux.sched_rr_get_interval.dir/sched_rr_get_interval.cpp.o.d -o libc/src/sched/linux/CMakeFiles/libc.src.sched.linux.sched_rr_get_interval.dir/sched_rr_get_interval.cpp.o -c /home/schrodingerzy/Documents/llvm/llvm-project/libc/src/sched/linux/sched_rr_get_interval.cpp
```
I can see the `-isystem` option, which does seemingly appear at the correct position. 

Inside the generated header directory:
```
 __llvm-libc-common.h   cmake_install.cmake   dirent.h   features.h   llvm-libc-macros   pthread.h   setjmp.h   stdlib.h    sys         time.h
 arpa                   CMakeFiles            errno.h    fenv.h       llvm-libc-types    sched.h     spawn.h    string.h    termios.h   unistd.h
 assert.h               ctype.h               fcntl.h    inttypes.h   math.h             search.h    stdio.h    strings.h   threads.h   wchar.h
```
It seems that `time.h`, `sched.h` are indeed there, not sure why `signal.h` is not generated.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzEWN1z4jgS_2ucF5UoY76ShzwAhllugKQSskzdi0tIbVszsuTTRwj7119JNgRIZu5u96qWSsV2f_9a3S3ZxBheSID7aDCJBukNcbZU-v6ZlloxLgvQ_yzdzU6xw_3qgH43VDFAVMmcF04Ty5VEudIoGsa0Ij8gGsZRbxzFaRSP_X34-26UbEmjSXODUJQkQaNzNAbPYC2XhYmSJOqN0ZlskF4uf19ls_V4spxlTy_rzWI1ez6KDs5Eg7DgO-qZyfSKQVVVcwEaa-v57w4G6YXwlcPHp4d_zKabnzukgsjiU49CsP_K03IxmWbzl-Uym7wslmnryWoH1-LT1fjrLJt9e3x42mTTh9XjYjnz19V4nT7_Qu_dzWI9Xb6ks-x5-pI-_CeNl-dZtlysv86ejuhPoK4DW47XX7J0Nh-_LDd_Sudps1xM3lWuVutatYH-lD1tmpw1eLLnzXidjpcP61m2XWx-y064f5XTD7a-bB-z8fN43SrlRJhfan3w3Yb02_hplv7SSFjO6bdv2cnccvyynv52nrwomTujo2S-4zJK5oZSQkv4LCmNtT9n69ibo_MSPXWqUU5TSLkGapU-nBvsR6PJXukfpiYU5kow0MHIXIjX6jxKT72cDs3jAlEipbIo55KbEtkSUO6E2DkuGCImEI7lgIyqoFR7VDshDOIycM3BWKhQCYSB9grEIicZ6IpLCBLNVBiZo0ynDSXpRoMJr0gBoTlvS2tr4-dYMo-SecFt6XYdqqoTnnDBtVbfgdoomRNjwJoomSdxN7697Y08bden3bskxqN-HuP-bhDj3ZDkmOY9mvSSu-5tsouSuzaE8H9zwthMVqqqikiGuDlmIFdCqD2XxccpuyOmPOKZl6qCsLSnMf7HIUrmqaKuAhlC_RxJyPepNNqpNomSCcLYEl2AjXrp2-0wG_axkz-k2kssuHRvuJAO4TSMl_V4NXt-HE9nUS_NMu8h86nPurdZnMVZwS3Ci78SpbeGMG9X_P-BVztpeQXm7BbvuDStsyiZc0mFY4Bw_riYIpxLhQ1URFpOMZcWdK0MD8uG81du-I4Lbg-YS8ElGFxyxkAivAWtlY56KSMWsHd0RnOycEQzYJi8Ei5Ia0PCHuEtEcKLvllNEN5KhZ10BhiuiSYVWNAIb_eaW8DGar-RIrylxFj8L0e8ZsWN4bLAOQfBMJfcciL4H75X8JZXteCUW5wTIWyplStKr69eQQPDZs8tLTGDnDhhG_dSwRuF2mJ7qCGQJH7l2joiMLPKh8NAgAX8Cce4ogBjsbevuU_rtokaUyVfQZuQSB-zAOJXFHPJQNqmMfCWWsJwRQ47wE4aV9dKW2AI54yTQipjOTWYKuGd5bmT1OthA-FqvByx5Oz5IUG4QDhdp7PJyxeEjWVRLy2ka6q_O0I4r7lf_VwDGEukD6opA19DlsvmoclJ60QqLMgbfg0D8wxZy3NyzyXDluwEtCRiDtIXsVTOfMbX1vIPtRDKJ6zWWep8ffJCXubzJ8t8XTbBsC9v70vC3pcwBpU3q-xz7UPCTf_htjNwTWzZriO1vses8qXhDdpSA2HYkBzsAeFtIdSOCB-bsdr57Jjj8Jg-PG6yx5fJcjHNHsfTr-Mvi_UXhFcpwqtNO8LnRtOm3YGFDpXuLUrm0xX5AXMu4Ni2HaNpJ0h1gkxzn2mdFWCz0LWvRHQY10drH3i0rjsK4dX8b3LdYQirvw02_UvD9ZdR_9Tvz88HyECzkUfD-Dj9o2GMVGi4KJmifclpiZgC42UrLgtxQKSugWhEbHuI0P4Ag47juoPOt-CFNH4aecECJGjip0pzXEDsdPL5sPm2j7N5dNuLJilqdj3sE4D9Lq5kp0Qo8OPobojCgSrj0lgiRCc8teyg7j1Je1IJtByIdRrMidqP7gbo3U1FqFbmXKNuuu7SjAH7vaqvaJYJvvO0M8vmYFD7e5f0-1WnPEMbRImuCfrwe-e_F-g1OxgFraV6996ila-BhD5H2wyWCxCh3stL06Yme3lluhlzV0Trj4nKXObFSW4su8Ab6P64p-0xvI-AqI_u5-ycSiuu_HNpA6TLACpiy0s75wtJNC0_YGP8OpXtWL-03JTGFXFPS6JPcK8a0IaOas_V0TBuS2EY-76LhnGbf9-PRAPy2zUw30jav_Egf7Y3TgPal4cgzgtJRCPPTWCfGq5zw-577K53R27gvjuKB8PRcJSMbsp7QvP-Du6S0Wgw7LEdoznc9kjSG96O4h6jyQ2_T-KkH3e7d91BPEhGnSEjdDccDVgXhr3-MI_6MVSEi46vpY7SxQ03xsH96HaUdG8E2YEw4WPI-0eEQXqj70Pp7Vxhon4suLHm3YDlVoQPKEFh4OvGb4_IKkSshaq2l68yBLVHTD_WNdEHxFyQvnyDuXFa3P_PryIBjR_JAdC_AwAA__9sZJJF">