Don't link math lib on Windows

examples/simple/CMakeLists.txt

@@ -2,4 +2,7 @@ project (simple C)
 include_directories(${CMAKE_BINARY_DIR}/include)
 link_directories(${CMAKE_BINARY_DIR})
 add_executable(simple simple.c)
-target_link_libraries(simple PRIVATE openhmd m)
+target_link_libraries(simple PRIVATE openhmd)
+if (UNIX)
+    target_link_libraries(simple PRIVATE m)
+endif()