Unlike fips_140_3, fips will be a (FIPS) version-agnostic build tag.
The listener support will remain in 140-3 only, but the IsFIPS() check
should apply regardless of FIPS version.
We add two FIPS-only build files which validate the constraints of FIPS
builds here: fips must be specified with either fips_140_2 or fips_140_3
build tags, and fips and cgo must also be specified together.
Additionally, using only a version-specific FIPS build tag without the
version-agnostic FIPS tag should be a failure.
Signed-off-by: Alexander Scheel <alex.scheel@hashicorp.com>
