Log Message:
gmp,mpfr: Remove CONFIGURE_ARGS flags from builtin.mk as it assumes that
all recursively depending packages can deal with them.
Those packages that need them already add those CONFIGURE_ARGS, at least
pbulk hasn't revealed any issues (thanks jperkin@).
XXX libiconv is in a similar position, so should receive similar
treatment, but at least it only adds the flags if GNU_CONFIGURE=yes
Fixes PR pkg/55487