[libc] Don't use Clang flags on other compilers

[gchatelet]

Summary

This is necessary to get llvm-libc compile with GCC.
This patch is extracted from D119002.

libc/src/string/CMakeLists.txt

 # - Declares an entry point,
 # - Attach the REQUIRE_CPU_FEATURES property to the target,
 # - Add the fully qualified target to `${name}_implementations` global property for tests.
 function(add_implementation name impl_name)
   cmake_parse_arguments(
     "ADD_IMPL"
     "" # Optional arguments
     "" # Single value arguments
-    "REQUIRE;SRCS;HDRS;DEPENDS;COMPILE_OPTIONS" # Multi value arguments
+    "REQUIRE;SRCS;HDRS;DEPENDS;COMPILE_OPTIONS;MLLVM_COMPILE_OPTIONS" # Multi value arguments
     ${ARGN})
+
+  if("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
+    list(APPEND ADD_IMPL_MLLVM_COMPILE_OPTIONS "-combiner-global-alias-analysis")
+    # Note that '-mllvm' needs to be prefixed with 'SHELL:' to prevent CMake flag deduplication.
+    foreach(opt IN LISTS ADD_IMPL_MLLVM_COMPILE_OPTIONS)
+      list(APPEND ADD_IMPL_COMPILE_OPTIONS "SHELL:-mllvm ${opt}")
+    endforeach()
+  endif()
+
   add_entrypoint_object(${impl_name}
     NAME ${name}
     SRCS ${ADD_IMPL_SRCS}
     HDRS ${ADD_IMPL_HDRS}
     DEPENDS ${ADD_IMPL_DEPENDS}
-    COMPILE_OPTIONS ${ADD_IMPL_COMPILE_OPTIONS} "SHELL:-mllvm -combiner-global-alias-analysis"
+    COMPILE_OPTIONS ${ADD_IMPL_COMPILE_OPTIONS}
   )
   get_fq_target_name(${impl_name} fq_target_name)
   set_target_properties(${fq_target_name} PROPERTIES REQUIRE_CPU_FEATURES "${ADD_IMPL_REQUIRE}")
   set_property(GLOBAL APPEND PROPERTY "${name}_implementations" "${fq_target_name}")
 endfunction()
 
 # ------------------------------------------------------------------------------
 # bcmp
if(${LIBC_TARGET_ARCHITECTURE_IS_X86})
   add_memcpy(memcpy_x86_64_opt_sse2   COMPILE_OPTIONS -march=k8             REQUIRE SSE2)
   add_memcpy(memcpy_x86_64_opt_sse4   COMPILE_OPTIONS -march=nehalem        REQUIRE SSE4_2)
   add_memcpy(memcpy_x86_64_opt_avx2   COMPILE_OPTIONS -march=haswell        REQUIRE AVX2)
   add_memcpy(memcpy_x86_64_opt_avx512 COMPILE_OPTIONS -march=skylake-avx512 REQUIRE AVX512F)
   add_memcpy(memcpy_opt_host          COMPILE_OPTIONS ${LIBC_COMPILE_OPTIONS_NATIVE})
   add_memcpy(memcpy)
 elseif(${LIBC_TARGET_ARCHITECTURE_IS_AARCH64})
   # Disable tail merging as it leads to lower performance.
-  # Note that '-mllvm' needs to be prefixed with 'SHELL:' to prevent CMake flag deduplication.
   add_memcpy(memcpy_opt_host          COMPILE_OPTIONS ${LIBC_COMPILE_OPTIONS_NATIVE}
-                                      COMPILE_OPTIONS "SHELL:-mllvm --tail-merge-threshold=0")
-  add_memcpy(memcpy                   COMPILE_OPTIONS "SHELL:-mllvm --tail-merge-threshold=0")
+                                      MLLVM_COMPILE_OPTIONS "-tail-merge-threshold=0")
+  add_memcpy(memcpy                   MLLVM_COMPILE_OPTIONS "-tail-merge-threshold=0")
 else()
   add_memcpy(memcpy_opt_host          COMPILE_OPTIONS ${LIBC_COMPILE_OPTIONS_NATIVE})
   add_memcpy(memcpy)
 endif()
 
 # ------------------------------------------------------------------------------
 # memmove
 # ------------------------------------------------------------------------------
if(${LIBC_TARGET_ARCHITECTURE_IS_X86})
   add_memmove(memmove_x86_64_opt_sse2   COMPILE_OPTIONS -march=k8             REQUIRE SSE2)
   add_memmove(memmove_x86_64_opt_sse4   COMPILE_OPTIONS -march=nehalem        REQUIRE SSE4_2)
   add_memmove(memmove_x86_64_opt_avx2   COMPILE_OPTIONS -march=haswell        REQUIRE AVX2)
   add_memmove(memmove_x86_64_opt_avx512 COMPILE_OPTIONS -march=skylake-avx512 REQUIRE AVX512F)
   add_memmove(memmove_opt_host          COMPILE_OPTIONS ${LIBC_COMPILE_OPTIONS_NATIVE})
   add_memmove(memmove)
 elseif(${LIBC_TARGET_ARCHITECTURE_IS_AARCH64})
   # Disable tail merging as it leads to lower performance.
-  # Note that '-mllvm' needs to be prefixed with 'SHELL:' to prevent CMake flag deduplication.
   add_memmove(memmove_opt_host          COMPILE_OPTIONS ${LIBC_COMPILE_OPTIONS_NATIVE}
-                                        COMPILE_OPTIONS "SHELL:-mllvm --tail-merge-threshold=0")
-  add_memmove(memmove                   COMPILE_OPTIONS "SHELL:-mllvm --tail-merge-threshold=0")
+                                        MLLVM_COMPILE_OPTIONS "-tail-merge-threshold=0")
+  add_memmove(memmove                   MLLVM_COMPILE_OPTIONS "-tail-merge-threshold=0")
 else()
   add_memmove(memmove_opt_host          COMPILE_OPTIONS ${LIBC_COMPILE_OPTIONS_NATIVE})
   add_memmove(memmove)
 endif()
 
 # ------------------------------------------------------------------------------
 # memset
 # ------------------------------------------------------------------------------

 if(${LIBC_TARGET_ARCHITECTURE_IS_X86})
   add_memset(memset_x86_64_opt_sse2   COMPILE_OPTIONS -march=k8             REQUIRE SSE2)
   add_memset(memset_x86_64_opt_sse4   COMPILE_OPTIONS -march=nehalem        REQUIRE SSE4_2)
   add_memset(memset_x86_64_opt_avx2   COMPILE_OPTIONS -march=haswell        REQUIRE AVX2)
   add_memset(memset_x86_64_opt_avx512 COMPILE_OPTIONS -march=skylake-avx512 REQUIRE AVX512F)
   add_memset(memset_opt_host          COMPILE_OPTIONS ${LIBC_COMPILE_OPTIONS_NATIVE})
   add_memset(memset)
 elseif(${LIBC_TARGET_ARCHITECTURE_IS_AARCH64})
+  # Disable tail merging as it leads to lower performance.
   add_memset(memset_opt_host          COMPILE_OPTIONS ${LIBC_COMPILE_OPTIONS_NATIVE}
-                                      COMPILE_OPTIONS "SHELL:-mllvm --tail-merge-threshold=0")
-  add_memset(memset                   COMPILE_OPTIONS "SHELL:-mllvm --tail-merge-threshold=0")
+                                      MLLVM_COMPILE_OPTIONS "-tail-merge-threshold=0")
+  add_memset(memset                   MLLVM_COMPILE_OPTIONS "-tail-merge-threshold=0")
 else()
   add_memset(memset_opt_host          COMPILE_OPTIONS ${LIBC_COMPILE_OPTIONS_NATIVE})
   add_memset(memset)
 endif()