Backport VST3 diagnostic pragma

Fixes excessive warnings when compiling on macOS.

This will be overwritten with the identical upstream fix
https://github.com/steinbergmedia/vst3_pluginterfaces/blob/master/base/falignpush.h
with the next tools/update_vst3.sh run

libs/vst3/pluginterfaces/base/falignpush.h

@@ -23,8 +23,6 @@
 	#else
 		#pragma pack(push, 1)
 	#endif
-	#pragma GCC diagnostic default "-Wpragma-pack"
-    #pragma GCC diagnostic default "-Wunknown-warning-option"
 #elif defined __BORLANDC__
 	#pragma -a8
 #elif SMTG_OS_WINDOWS