[CMake] Avoid passing -rtlib=compiler-rt when using compiler-rt

We build libc++ and libc++abi with -nodefaultlibs, so -rtlib=compiler-rt
has no effect and results in an 'argument unused during compilation'
warning which breaks the build when using -Werror. We can therefore drop
-rtlib=compiler-rt without any functional change; note that the actual
compiler-rt linking is handled by HandleCompilerRT.

Differential Revision: https://reviews.llvm.org/D58084

llvm-svn: 353786

libcxx/CMakeLists.txt

@@ -485,10 +485,6 @@ endif()
 # Configure compiler.
 include(config-ix)
 
-if (LIBCXX_USE_COMPILER_RT)
-  list(APPEND LIBCXX_LINK_FLAGS "-rtlib=compiler-rt")
-endif()
-
 # Configure coverage options.
 if (LIBCXX_GENERATE_COVERAGE)
   include(CodeCoverage)

libcxxabi/CMakeLists.txt

@@ -262,10 +262,6 @@ if (LIBCXXABI_HAS_NOSTDINCXX_FLAG)
   string(REPLACE "-stdlib=libstdc++" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
 endif()
 
-if (LIBCXXABI_USE_COMPILER_RT)
-  list(APPEND LIBCXXABI_LINK_FLAGS "-rtlib=compiler-rt")
-endif()
-
 # Let the library headers know they are currently being used to build the
 # library.
 add_definitions(-D_LIBCXXABI_BUILDING_LIBRARY)