From 223ed705d0d3c3b07f00202a04447df836c05df8 Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne@apple.com>
Date: Thu, 2 May 2019 17:43:48 +0000
Subject: [PATCH] [libc++][CMake] Link against libSystem on Apple platforms

Instead of manually linking against libm/librt/libpthread, we should be
linking against libSystem on Apple platforms, and only that. libm and
libpthread are symlinks to libSystem anyway.

llvm-svn: 359808
---
 libcxx/cmake/config-ix.cmake | 7 +++++++
 libcxx/src/CMakeLists.txt    | 4 ++++
 2 files changed, 11 insertions(+)

diff --git a/libcxx/cmake/config-ix.cmake b/libcxx/cmake/config-ix.cmake
index 730ee7e164a6..23ae71025e54 100644
--- a/libcxx/cmake/config-ix.cmake
+++ b/libcxx/cmake/config-ix.cmake
@@ -80,8 +80,15 @@ if(WIN32 AND NOT MINGW)
   set(LIBCXX_HAS_PTHREAD_LIB NO)
   set(LIBCXX_HAS_M_LIB NO)
   set(LIBCXX_HAS_RT_LIB NO)
+  set(LIBCXX_HAS_SYSTEM_LIB NO)
+elseif(APPLE)
+  check_library_exists(System write "" LIBCXX_HAS_SYSTEM_LIB)
+  set(LIBCXX_HAS_PTHREAD_LIB NO)
+  set(LIBCXX_HAS_M_LIB NO)
+  set(LIBCXX_HAS_RT_LIB NO)
 else()
   check_library_exists(pthread pthread_create "" LIBCXX_HAS_PTHREAD_LIB)
   check_library_exists(m ccos "" LIBCXX_HAS_M_LIB)
   check_library_exists(rt clock_gettime "" LIBCXX_HAS_RT_LIB)
+  set(LIBCXX_HAS_SYSTEM_LIB NO)
 endif()
diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
index 3c31548c2c4c..5d9cc01d165f 100644
--- a/libcxx/src/CMakeLists.txt
+++ b/libcxx/src/CMakeLists.txt
@@ -140,6 +140,10 @@ function(cxx_link_system_libraries target)
   target_add_compile_flags_if_supported(${target} PRIVATE "/Zl")
   target_add_link_flags_if_supported(${target} PRIVATE "/nodefaultlib")
 
+  if (LIBCXX_HAS_SYSTEM_LIB)
+    target_link_libraries(${target} PUBLIC System)
+  endif()
+
   if (LIBCXX_HAS_PTHREAD_LIB)
     target_link_libraries(${target} PUBLIC pthread)
   endif()