Add convenience functions to CMakeLists.txt

The helper functions allow setting compiler flags only if compiler
supports them.

CMakeLists.txt

@@ -60,8 +60,44 @@ execute_process(
 )
 add_definitions(-DOPENRCT2_COMMIT_SHA1_SHORT="${OPENRCT2_COMMIT_SHA1_SHORT}")
 
+# Convenience functions to set compiler flags only if available
+include(CheckCCompilerFlag)
+include(CheckCXXCompilerFlag)
+
+function(ADD_CHECK_C_COMPILER_FLAG
+    _CFLAGS
+    _CACHE_VAR
+    _FLAG
+    )
+
+    CHECK_C_COMPILER_FLAG("${_FLAG}" "${_CACHE_VAR}")
+    if(${_CACHE_VAR})
+        # message(STATUS "Using CFLAG: ${_FLAG}")
+        set(${_CFLAGS} "${${_CFLAGS}} ${_FLAG}" PARENT_SCOPE)
+    else()
+        message(STATUS "Unsupported CFLAG: ${_FLAG}")
+    endif()
+endfunction()
+
+function(ADD_CHECK_CXX_COMPILER_FLAG
+    _CXXFLAGS
+    _CACHE_VAR
+    _FLAG
+    )
+
+    CHECK_CXX_COMPILER_FLAG("${_FLAG}" "${_CACHE_VAR}")
+    if(${_CACHE_VAR})
+        # message(STATUS "Using CXXFLAG: ${_FLAG}")
+        set(${_CXXFLAGS} "${${_CXXFLAGS}} ${_FLAG}" PARENT_SCOPE)
+    else()
+        message(STATUS "Unsupported CXXFLAG: ${_FLAG}")
+    endif()
+endfunction()
+
+# pkg-config
 INCLUDE(FindPkgConfig)
 
+# Needed for linking with non-broken OpenSSL on Apple platforms
 if (APPLE)
 	set(ENV{PKG_CONFIG_PATH} "$ENV{PKG_CONFIG_PATH}:/usr/local/opt/openssl/lib/pkgconfig")
 endif (APPLE)