Makefile: consider GOHOSTFLAGS for ENV variable and descriptions target #17528

Job	Run time
build	3m 26s
race	7m 8s
dashboard	2m 8s
race_dashboard	3m 17s
aux	4m 43s
arch (presubmit_arch_netbsd)	3m 47s
old	6m 55s
arch (presubmit_arch_linux)	10m 20s
arch (presubmit_arch_executor)	3m 16s
arch (presubmit_arch_freebsd)	6m 27s
arch (presubmit_arch_openbsd)	3m 35s
arch (presubmit_arch_darwin)	3m 47s
arch (presubmit_arch_windows)	3m 32s
gvisor	3m 56s
	1h 6m 17s

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