Go: Add `-gcflags` to `std_go_args` #30880

Job	Run time
syntax	40s
cask audit	2m 37s
tap syntax	6m 49s
formula audit	4m 36s
test default formula (Ubuntu 22.04)	1m 37s
tests (online)	5m 18s
test default formula (Ubuntu 20.04)	2m 48s
update-test (Ubuntu 22.04)	25s
tests (generic OS)	2m 56s
vendored gems	34s
test default formula (macOS 13 x86_64)	3m 54s
update-test (macOS)	28s
tests (Ubuntu 22.04)	3m 4s
test default formula (macOS 15 arm64)	1m 19s
tests (Ubuntu 20.04)	4m 9s
tests (macOS 13 x86_64)	7m 52s
tests (macOS 15 arm64)	5m 1s
	54m 7s

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