Better MinGW build support (#921)

test/CMakeLists.txt

@@ -229,7 +229,7 @@ target_link_libraries(
     $<$<AND:$<PLATFORM_ID:Windows>,$<BOOL:MINGW>>:psapi>
 )
 
-if(MSVC)
+if(WIN32)
     target_compile_definitions(
         mbgl-test
         PRIVATE MBGL_BUILDING_LIB

test/style/style_parser.test.cpp

@@ -13,7 +13,7 @@
 #include <fstream>
 #include <set>
 
-#if defined(_MSC_VER) && !defined(__clang__)
+#if defined(WIN32) && !defined(__clang__)
 #include <Windows.h>
 #ifdef GetObject
 #undef GetObject
@@ -97,7 +97,7 @@ static void populateNames(std::vector<std::string>& names) {
         }
     };
 
-#if defined(_MSC_VER) && !defined(__clang__)
+#if defined(WIN32) && !defined(__clang__)
     style_directory += "/*";
     WIN32_FIND_DATAA ffd;
     HANDLE hFind = FindFirstFileA(style_directory.c_str(), &ffd);