test-input: avoid w32-pthreads for mingw-w64

test/test-input/CMakeLists.txt

@@ -2,7 +2,7 @@ project(test-input)
 
 include_directories(SYSTEM "${CMAKE_SOURCE_DIR}/libobs")
 
-if(WIN32)
+if(MSVC)
 	set(test-input_PLATFORM_DEPS
 		w32-pthreads)
 endif()