[CMake] Change the flag to use compiler-rt builtins to boolean

[phosek]

Summary

This changes the name and the type to what it was prior to r333037
which matches the name of the flag used in other runtimes: libc++,
libc++abi and libunwind. We don't need the type to be a string since
there's only binary choice between libgcc and compiler-rt unlike in
the case of C++ library where there're multiple options.

[phosek]

compiler-rt/CMakeLists.txt

159–160

@beanz do you know if we could also default to ON on APPLE?

165

I'm not a big fan of the name, but another alternative would be COMPILER_RT_USE_COMPILER_RT which isn't great either.

[morehouse]

compiler-rt/CMakeLists.txt

163

Maybe this would be simpler:

set(SANITIZER_DEFAULT_COMPILER_RT OFF)
if (FUCHSIA)
  set(SANITIZER_DEFAULT_COMPILER_RT ON)
endif()

165

COMPILER_RT_USE_BUILTIN_RUNTIME_LIBRARY?

compiler-rt/CMakeLists.txt

if (SANITIZER_CXX_ABI STREQUAL "default")
   else()
     set(SANITIZER_CXX_ABI_LIBNAME "libstdc++")
     set(SANITIZER_CXX_ABI_SYSTEM 1)
   endif()
 else()
   set(SANITIZER_CXX_ABI_LIBNAME "${SANITIZER_CXX_ABI}")
   set(SANITIZER_CXX_ABI_SYSTEM 1)
 endif()
 
-set(COMPILER_RT_RUNTIME "default" CACHE STRING
-    "Compiler runtime to use.")
-
-if (COMPILER_RT_RUNTIME STREQUAL "default")
-  if (FUCHSIA)
-    set(COMPILER_RT_RUNTIME_LIBRARY "builtins")
-  endif()
-else()
-  set(COMPILER_RT_RUNTIME_LIBRARY "${COMPILER_RT_RUNTIME}")
+set(DEFAULT_COMPILER_RT_USE_BUILTINS_LIBRARY OFF)
+  set(DEFAULT_COMPILER_RT_USE_BUILTINS_LIBRARY ON)
 endif()
 
+option(COMPILER_RT_USE_BUILTINS_LIBRARY
+  "Use compiler-rt builtins instead of libgcc" ${DEFAULT_COMPILER_RT_USE_BUILTINS_LIBRARY})
+
 include(config-ix)
 
 #================================
 # Setup Compiler Flags
 #================================
 
 if(MSVC)
   # Override any existing /W flags with /W4. This is what LLVM does.  Failing to

 append_list_if(COMPILER_RT_HAS_WD4291_FLAG /wd4291 SANITIZER_COMMON_CFLAGS)
 append_list_if(COMPILER_RT_HAS_WD4391_FLAG /wd4391 SANITIZER_COMMON_CFLAGS)
 append_list_if(COMPILER_RT_HAS_WD4722_FLAG /wd4722 SANITIZER_COMMON_CFLAGS)
 append_list_if(COMPILER_RT_HAS_WD4800_FLAG /wd4800 SANITIZER_COMMON_CFLAGS)
 
 # Set common link flags.
 append_list_if(COMPILER_RT_HAS_NODEFAULTLIBS_FLAG -nodefaultlibs SANITIZER_COMMON_LINK_FLAGS)
 
-if (COMPILER_RT_RUNTIME_LIBRARY STREQUAL "builtins")
+if (COMPILER_RT_USE_BUILTINS_LIBRARY)
   list(APPEND SANITIZER_COMMON_LINK_LIBS ${COMPILER_RT_BUILTINS_LIBRARY})
 else()
   if (ANDROID)
     append_list_if(COMPILER_RT_HAS_GCC_LIB gcc SANITIZER_COMMON_LINK_LIBS)
   else()
     append_list_if(COMPILER_RT_HAS_GCC_S_LIB gcc_s SANITIZER_COMMON_LINK_LIBS)
   endif()
 endif()

compiler-rt/cmake/config-ix.cmake

 include(CMakePushCheckState)
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 include(CheckLibraryExists)
 include(CheckSymbolExists)
 include(TestBigEndian)
 
 function(check_linker_flag flag out_var)
   cmake_push_check_state()
   set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} ${flag}")
   check_cxx_compiler_flag("" ${out_var})
   cmake_pop_check_state()
 endfunction()
 
 check_library_exists(c fopen "" COMPILER_RT_HAS_LIBC)
-if (COMPILER_RT_RUNTIME_LIBRARY STREQUAL "builtins")
+if (COMPILER_RT_USE_BUILTINS_LIBRARY)
   include(HandleCompilerRT)
   find_compiler_rt_library(builtins COMPILER_RT_BUILTINS_LIBRARY)
 else()
   if (ANDROID)
     check_library_exists(gcc __gcc_personality_v0 "" COMPILER_RT_HAS_GCC_LIB)
   else()
     check_library_exists(gcc_s __gcc_personality_v0 "" COMPILER_RT_HAS_GCC_S_LIB)
   endif()
 endif()
 
 check_c_compiler_flag(-nodefaultlibs COMPILER_RT_HAS_NODEFAULTLIBS_FLAG)
 if (COMPILER_RT_HAS_NODEFAULTLIBS_FLAG)
   set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nodefaultlibs")
   if (COMPILER_RT_HAS_LIBC)
     list(APPEND CMAKE_REQUIRED_LIBRARIES c)
   endif ()
-  if (COMPILER_RT_RUNTIME_LIBRARY STREQUAL "builtins")
+  if (COMPILER_RT_USE_BUILTINS_LIBRARY)
     list(APPEND CMAKE_REQUIRED_LIBRARIES "${COMPILER_RT_BUILTINS_LIBRARY}")
   elseif (COMPILER_RT_HAS_GCC_S_LIB)
     list(APPEND CMAKE_REQUIRED_LIBRARIES gcc_s)
   elseif (COMPILER_RT_HAS_GCC_LIB)
     list(APPEND CMAKE_REQUIRED_LIBRARIES gcc)
   endif ()
 endif ()