gvariant-core.c: Fix suffix alignment on 32-bit MSVC builds

With a similar rationale to commit d50102f2, this avoids the static
assert from failing on 32-bit Visual Studio builds.

glib/gvariant-core.c

@@ -78,6 +78,8 @@ struct _GVariant
 
 #if g_macro__has_attribute(aligned)
   guint8 suffix[] __attribute__((aligned(8)));
+#elif defined _MSC_VER
+  __declspec(align (8)) guint8 suffix[];
 #else
   guint8 suffix[];
 #endif