[libc] Fix builds on Windows

[Lancern]

This PR changes several places in the CMake scripts to make libc build on Windows. It adds the errno entrypoint to the Windows target.

A mistake in the overlay build doc is also fixed.

Tests still cannot be built on Windows because of the lack of osutils.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Sirui Mu (Lancern)

Changes

This PR changes several places in the CMake scripts to make libc build on Windows. It adds the errno entrypoint to the Windows target.

A mistake in the overlay build doc is also fixed.

Tests still cannot be built on Windows because of the lack of osutils.

---

Full diff: https://github.com/llvm/llvm-project/pull/102162.diff

3 Files Affected:

• (modified) libc/cmake/modules/LLVMLibCTestRules.cmake (+1-1)
• (modified) libc/config/windows/entrypoints.txt (+3)
• (modified) libc/docs/overlay_mode.rst (+1-1)

diff --git a/libc/cmake/modules/LLVMLibCTestRules.cmake b/libc/cmake/modules/LLVMLibCTestRules.cmake
index 539ed0429549f..d8097855d1637 100644
--- a/libc/cmake/modules/LLVMLibCTestRules.cmake
+++ b/libc/cmake/modules/LLVMLibCTestRules.cmake
@@ -348,7 +348,7 @@ function(add_libc_fuzzer target_name)
 endfunction(add_libc_fuzzer)
 
 # Get libgcc_s to be used in hermetic and integration tests.
-if(NOT LIBC_CC_SUPPORTS_NOSTDLIBPP)
+if(NOT MSVC AND NOT LIBC_CC_SUPPORTS_NOSTDLIBPP)
   execute_process(COMMAND ${CMAKE_CXX_COMPILER} -print-file-name=libgcc_s.so.1
                   OUTPUT_VARIABLE LIBGCC_S_LOCATION)
   string(STRIP ${LIBGCC_S_LOCATION} LIBGCC_S_LOCATION)
diff --git a/libc/config/windows/entrypoints.txt b/libc/config/windows/entrypoints.txt
index d66e7f1fed81f..f66438061ef4b 100644
--- a/libc/config/windows/entrypoints.txt
+++ b/libc/config/windows/entrypoints.txt
@@ -92,6 +92,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdlib.realloc
     libc.src.stdlib.aligned_alloc
     libc.src.stdlib.free
+
+    # errno.h entrypoints
+    libc.src.errno.errno
 )
 
 set(TARGET_LIBM_ENTRYPOINTS
diff --git a/libc/docs/overlay_mode.rst b/libc/docs/overlay_mode.rst
index f9b566658bb49..37368ffc1fea1 100644
--- a/libc/docs/overlay_mode.rst
+++ b/libc/docs/overlay_mode.rst
@@ -39,7 +39,7 @@ the CMake configure step as follows:
   $> cd llvm-project  # The llvm-project checkout
   $> mkdir build
   $> cd build
-  $> cmake ../llvm -G Ninja -DLLVM_ENABLE_PROJECTS="libc"  \
+  $> cmake ../llvm -G Ninja -DLLVM_ENABLE_RUNTIMES="libc"  \
      -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ \
      -DCMAKE_BUILD_TYPE=<Debug|Release>                    \  # Select build type
      -DCMAKE_INSTALL_PREFIX=<Your prefix of choice>           # Optional

[SchrodingerZhu]

As a side note, LLVM_ENABLE_PROJECTS should work but the cmake is unhappy about it, generating no targets of libc for some reasons. I think it is generally better to use LLVM_ENABLE_RUNTIMES after all.

[SchrodingerZhu]

LGTM

[SchrodingerZhu]

Confirmed locally on my machine. Thank you for the patch!