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[CMake] Use __libc_start_main rather than fopen when checking for C library

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The check_library_exists CMake uses a custom symbol definition. This
is a problem when checking for C library symbols because Clang
recognizes many of them as builtins, and returns the
-Wbuiltin-requires-header (or -Wincompatible-library-redeclaration)
error. When building with -Werror which is the default, this causes
the check_library_exists check fail making the build think that C
library isn't available.

To avoid this issue, we should use a symbol that isn't recognized by
Clang and wouldn't cause the same issue. __libc_start_main seems like
reasonable choice that fits the bill.

Differential Revision: https://reviews.llvm.org/D57142

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@352341 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Petr Hosek
2019-01-28 04:12:54 +00:00
parent 427fc9484c
commit e15f28cfca
1 changed files with 1 additions and 1 deletions
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cmake/config-ix.cmake
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@@ -7,7 +7,7 @@ if(WIN32 AND NOT MINGW)
# let the default linking take care of that. # let the default linking take care of that.
set(LIBCXX_HAS_C_LIB NO) set(LIBCXX_HAS_C_LIB NO)
else() else()
check_library_exists(c fopen "" LIBCXX_HAS_C_LIB) check_library_exists(c __libc_start_main "" LIBCXX_HAS_C_LIB)
endif() endif()
if (NOT LIBCXX_USE_COMPILER_RT) if (NOT LIBCXX_USE_COMPILER_RT)