cmd/compile: skip types.Sym for GC mask symbols
cmd/compile: skip types.Sym for GC mask symbols

For GC mask symbols, we don't need to create types.Sym, just the
LSym.

Change-Id: I285b518cfd60bfaa3202a02b3005a7122daeb338
Reviewed-on: https://go-review.googlesource.com/c/go/+/313512
Trust: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Run-TryBot: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>

nawawi/go,cloudflare/go,nawawi/go,cloudflare/go,CAFxX/go,cloudflare/go,golang/go,cloudflare/go,golang/go,nawawi/go,golang/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,golang/go,golang/go,cloudflare/go,CAFxX/go,nawawi/go,CAFxX/go,cloudflare/go,nawawi/go,CAFxX/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,nawawi/go,golang/go,CAFxX/go,cloudflare/go