macOS: fix build with new cmake versions

Change-Id: I2da7cc048ecceacc9f26ee1a5084b4e86110e4e9
Reviewed-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>

contrib/src/main.mak

@@ -475,9 +475,9 @@ ifdef HAVE_WIN32
 endif
 ifdef HAVE_DARWIN_OS
 	echo "set(CMAKE_SYSTEM_NAME Darwin)" >> $@
-	echo "set(CMAKE_C_FLAGS $(CFLAGS))" >> $@
-	echo "set(CMAKE_CXX_FLAGS $(CFLAGS))" >> $@
-	echo "set(CMAKE_LD_FLAGS $(LDFLAGS))" >> $@
+	echo "set(CMAKE_C_FLAGS \"$(CFLAGS)\")" >> $@
+	echo "set(CMAKE_CXX_FLAGS \"$(CXXFLAGS)\")" >> $@
+	echo "set(CMAKE_LD_FLAGS \"$(LDFLAGS)\")" >> $@
 	echo "set(CMAKE_AR ar CACHE FILEPATH "Archiver")" >> $@
 ifdef HAVE_IOS
 	echo "set(CMAKE_OSX_SYSROOT $(IOS_SDK))" >> $@