build: fix g++ hard dependency on FreeBSD
build: fix g++ hard dependency on FreeBSD

Signed-off-by: Dave Cottlehuber <9174ef3e93199eb9960513de3be6e82218a49db6@skunkwerks.at>

janestreet/re2,skunkwerks/re2,skunkwerks/re2,skunkwerks/re2,skunkwerks/re2,janestreet/re2,janestreet/re2,janestreet/re2,janestreet/re2,skunkwerks/re2,skunkwerks/re2,janestreet/re2