cmd/dist: fix build failure of misc/cgo/test on arm64
misc/cgo/test fails in 'dist test' on arm64 if the C compiler is of GCC-9.4 or
above and its 'outline atomics' feature is enabled, since the internal linking
hasn't yet supported "__attribute__((constructor))" and also mis-handles hidden
visibility.
This change addresses the problem by skipping the internal linking cases of
misc/cgo/test on linux/arm64. It fixes 'dist test' failure only, user is expected to
pass a GCC option '-mno-outline-atomics' via CGO_CFLAGS if running into the same
problem when building cgo programs using internal linking.