[compiler-rt] Use flags found when configuring builtins during compilation

[fjricci]

Summary

This fixes the omission of -fPIC when building the builtins.

[beanz]

LGTM

[fjricci]

This change breaks on certain sysroots, because of -ffreestanding. I removed that flag in rL279496, after verifying that the non-standalone build also doesn't add this flag by default.

cmake/builtin-config-ix.cmake

 include(BuiltinTests)
 include(CheckCSourceCompiles)
 
 # Make all the tests only check the compiler
 set(TEST_COMPILE_ONLY On)
 
 builtin_check_c_compiler_flag(-fPIC                 COMPILER_RT_HAS_FPIC_FLAG)
 builtin_check_c_compiler_flag(-fPIE                 COMPILER_RT_HAS_FPIE_FLAG)
 builtin_check_c_compiler_flag(-fno-builtin          COMPILER_RT_HAS_FNO_BUILTIN_FLAG)
 builtin_check_c_compiler_flag(-std=c99              COMPILER_RT_HAS_STD_C99_FLAG)
 builtin_check_c_compiler_flag(-fvisibility=hidden   COMPILER_RT_HAS_VISIBILITY_HIDDEN_FLAG)
 builtin_check_c_compiler_flag(-fomit-frame-pointer  COMPILER_RT_HAS_OMIT_FRAME_POINTER_FLAG)
 builtin_check_c_compiler_flag(-ffreestanding        COMPILER_RT_HAS_FREESTANDING_FLAG)
-builtin_check_c_compiler_flag(-mfloat-abi=soft      COMPILER_RT_HAS_FLOAT_ABI_SOFT_FLAG)
-builtin_check_c_compiler_flag(-mfloat-abi=hard      COMPILER_RT_HAS_FLOAT_ABI_HARD_FLAG)
-builtin_check_c_compiler_flag(-static               COMPILER_RT_HAS_STATIC_FLAG)
 
 builtin_check_c_compiler_source(COMPILER_RT_HAS_ATOMIC_KEYWORD
 "
 int foo(int x, int y) {
  _Atomic int result = x * y;
  return result;
 }
 ")

lib/builtins/CMakeLists.txt

 add_custom_target(builtins)
 set_target_properties(builtins PROPERTIES FOLDER "Compiler-RT Misc")
 
 if (APPLE)
   add_subdirectory(Darwin-excludes)
   add_subdirectory(macho_embedded)
   darwin_add_builtin_libraries(${BUILTIN_SUPPORTED_OS})
 else ()
-  append_string_if(COMPILER_RT_HAS_STD_C99_FLAG -std=gnu99 maybe_stdc99)
+  set(BUILTIN_CFLAGS "")
+  append_list_if(COMPILER_RT_HAS_STD_C99_FLAG -std=gnu99 BUILTIN_CFLAGS)
+
+  # These flags would normally be added to CMAKE_C_FLAGS by the llvm
+  # cmake step. Add them manually if this is a standalone build.
+  if(COMPILER_RT_STANDALONE_BUILD)
+    append_list_if(COMPILER_RT_HAS_FPIC_FLAG -fPIC BUILTIN_CFLAGS)
+    append_list_if(COMPILER_RT_HAS_FNO_BUILTIN_FLAG -fno-builtin BUILTIN_CFLAGS)
+    append_list_if(COMPILER_RT_HAS_VISIBILITY_HIDDEN_FLAG -fvisibility=hidden BUILTIN_CFLAGS)
+    if(NOT COMPILER_RT_DEBUG)
+      append_list_if(COMPILER_RT_HAS_OMIT_FRAME_POINTER_FLAG -fomit-frame-pointer BUILTIN_CFLAGS)
+    endif()
+    append_list_if(COMPILER_RT_HAS_FREESTANDING_FLAG -ffreestanding BUILTIN_CFLAGS)
+  endif()
 
   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
     if (CAN_TARGET_${arch})
       # Filter out generic versions of routines that are re-implemented in
       # architecture specific manner.  This prevents multiple definitions of the
       # same symbols, making the symbol selection non-deterministic.
       foreach (_file ${${arch}_SOURCES})
         if (${_file} MATCHES ${arch}/*)
           get_filename_component(_name ${_file} NAME)
           string(REPLACE ".S" ".c" _cname "${_name}")
           list(REMOVE_ITEM ${arch}_SOURCES ${_cname})
         endif ()
       endforeach ()
 
       add_compiler_rt_runtime(clang_rt.builtins
                               STATIC
                               ARCHS ${arch}
                               SOURCES ${${arch}_SOURCES}
-                              CFLAGS ${maybe_stdc99}
+                              CFLAGS ${BUILTIN_CFLAGS}
                               PARENT_TARGET builtins)
     endif ()
   endforeach ()
 endif ()
 
 add_dependencies(compiler-rt builtins)