Extended Description

Clang IAS supports -Wa,-defsym,FOO=BAR but not -Wa,--defsym,FOO=BAR (with two -s). GNU as accepts both but documents the --defsym FOO=BAR form so it is presumably preferred.

(We are attempting to retire use of GNU as 2.17.50 in FreeBSD. Most assembly files in our tree are already assembled by Clang IAS but there are a small number that still use GNU as for on reason or another, listed in https://bugs.freebsd.org/233611.)