Fixed force cxx version tests

test/core/core_force_cxx03.cpp

@@ -1,4 +1,6 @@
-#define GLM_FORCE_CXX03
+#ifndef GLM_FORCE_CXX03
+#	define GLM_FORCE_CXX03
+#endif
 
 #include <glm/glm.hpp>
 #include <glm/ext.hpp>

test/core/core_force_cxx11.cpp

@@ -1,4 +1,6 @@
-#define GLM_FORCE_CXX11
+#ifndef GLM_FORCE_CXX11
+#	define GLM_FORCE_CXX11
+#endif
 
 #include <glm/glm.hpp>
 #include <glm/ext.hpp>

test/core/core_force_cxx98.cpp

@@ -1,4 +1,6 @@
-#define GLM_FORCE_CXX98
+#ifndef GLM_FORCE_CXX98
+#	define GLM_FORCE_CXX98
+#endif
 
 #include <glm/glm.hpp>
 #include <glm/ext.hpp>