Fixing up the compiler options for Windows.

Author: rmpowell77

CMakeLists.txt

@@ -5,7 +5,10 @@ set (munkres-cpp_VERSION_MAJOR 2)
 set (munkres-cpp_VERSION_MINOR 0)
 
 set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
-set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra")
+# https://stackoverflow.com/questions/2274006/cmake-invalid-numeric-argument-wextra
+if(CMAKE_COMPILER_IS_GNUCXX)
+    set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra")
+endif(CMAKE_COMPILER_IS_GNUCXX)
 set (CMAKE_CXX_FLAGS_DEBUG   "${CMAKE_CXX_FLAGS} -O0 -ggdb3 -DDEBUG")
 set (CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS} -O3")