follow-up to c0092c7 - fix macos build warnings

CMakeLists.txt

@@ -1,12 +1,21 @@
 # Project
 cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
 project(heapusage VERSION 1.0 LANGUAGES C CXX)
-set(COMMON_FLAGS "-funwind-tables -g -Wall -Wextra -Wpedantic -Wshadow -Wpointer-arith \
-                  -Wcast-qual -Wno-missing-braces -Wswitch-default -Wcast-align \
-                  -Wunreachable-code -Wuninitialized -Wno-stringop-overflow")
-set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99 ${COMMON_FLAGS} -Wstrict-prototypes \
-                   -Wmissing-prototypes")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${COMMON_FLAGS}")
+
+set(COMMON_FLAGS "-funwind-tables -g -Wall -Wextra -Wpedantic -Wshadow \
+                  -Wpointer-arith -Wcast-qual -Wno-missing-braces \
+                  -Wswitch-default -Wcast-align -Wunreachable-code \
+                  -Wuninitialized")
+
+if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+  set(TOOLCHAIN_FLAGS "")
+elseif (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+  set(TOOLCHAIN_FLAGS "-Wno-stringop-overflow")
+endif()
+
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99 ${COMMON_FLAGS} ${TOOLCHAIN_FLAGS} \
+                   -Wstrict-prototypes -Wmissing-prototypes")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${COMMON_FLAGS} ${TOOLCHAIN_FLAGS}")
 
 # C++ compiler flags
 set(CMAKE_CXX_STANDARD 11)