Merge pull request #22 from orbea/clang

cmake: Silence warnings with clang.

CMakeLists.txt

@@ -81,16 +81,13 @@ endif()
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-    include(CheckCXXCompilerFlag)
-    CHECK_CXX_COMPILER_FLAG("-Wall" COMPILER_SUPPORTS_WALL)
-    if(COMPILER_SUPPORTS_WALL)
-      message("Enabling -Wall")
-      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall")
-    endif()
+    include(CheckCXXFlag)
+    check_cxx_flag(-Wall COMPILER_SUPPORTS_WALL)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wno-switch")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-switch")
     if(NOT ANDROID)
-      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-class-memaccess -Wno-invalid-offsetof")
+      check_cxx_flag(-Wno-class-memaccess COMPILER_SUPPORTS_MEMACCESS)
+      check_cxx_flag(-Wno-invalid-offsetof COMPILER_SUPPORTS_OFFSETOF)
     endif()
 endif()
 

CMakeModules/CheckCXXFlag.cmake

@@ -0,0 +1,8 @@
+include(CheckCXXCompilerFlag)
+
+function(check_cxx_flag flag var)
+    CHECK_CXX_COMPILER_FLAG("-Werror ${flag}" ${var})
+    if(${var})
+       set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${flag}" PARENT_SCOPE)
+    endif()
+endfunction()