Fixed Visual Studio compiler warning (#30)

* Fixed Visual Studio compiler warning

"#pragma GCC" causes warning 4068 "Unknown pragma" when compiling with Visual Studio 2022.
Maybe the condition should be
    #if defined(__GNUC__) || defined(__clang__)
instead. Both are used in the other files.

* Fixed Visual Studio compiler warning

Replaced
    #if defined(__GNUC__)
by
    #if defined(__GNUC__) || defined(__clang__)

include/gtl/vector.hpp

@@ -1311,10 +1311,14 @@ class vector {
             impl_.e_ += n;
         } else {
             if constexpr (std::is_trivially_copyable_v<T> && usingStdAllocator) {
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wnonnull" // disable erroneous warning
+#if defined(__GNUC__) || defined(__clang__)
+    #pragma GCC diagnostic push
+    #pragma GCC diagnostic ignored "-Wnonnull" // disable erroneous warning
+#endif
                 std::memmove((void*)(position + n), (void*)position, tail * sizeof(T));
-#pragma GCC diagnostic pop
+#if defined(__GNUC__) || defined(__clang__)
+    #pragma GCC diagnostic pop
+#endif
                 impl_.e_ += n;
             } else {
                 D_uninitialized_move_a(impl_.e_, impl_.e_ - n, impl_.e_);