Use nicer CMake functions for enabling LTO

Signed-off-by: Juan Cruz Viotti <[email protected]>

Author: jviotti

cmake/common/defaults.cmake

@@ -97,20 +97,21 @@ endif()
 # Note we don't enable LTO on RelWithDebInfo, as it breaks debugging symbols
 # on at least AppleClang, making stepping through source code impossible.
 
+# LTO is applied globally because it is a whole-program optimization.
+# Every translation unit must be compiled with LTO flags for the linker
+# to perform cross-module optimization effectively.
 if(CMAKE_BUILD_TYPE STREQUAL "Release")
   if(SOURCEMETA_COMPILER_GCC AND NOT BUILD_SHARED_LIBS)
     message(STATUS "Enabling Fat LTO")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -flto -ffat-lto-objects")
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -flto")
-    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -flto")
+    add_compile_options(-flto -ffat-lto-objects)
+    add_link_options(-flto)
   endif()
 
   # TODO: Make this work on Linux on LLVM
   if(SOURCEMETA_COMPILER_LLVM AND NOT BUILD_SHARED_LIBS AND APPLE)
     message(STATUS "Enabling Fat LTO")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -flto=full")
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -flto=full")
-    set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -flto=full")
+    add_compile_options(-flto=full)
+    add_link_options(-flto=full)
   endif()
 endif()