Update crypto/fips to use generated rules, prereqs

This change preserves the same behavior and output as before, except that it
replaces the shell-based subdir-building recipe with generated rules and
prerequisites. This doesn't eliminate the recursive make, but refactors it so
that eliminating it will be more straightforward when the time comes.
Prefix fipsas.pl with FIPSCANISTERINTERNAL env var

This is in preparation for removing BUILDENV from Makefile.fips.
fipsdist.pl: replace BUILDENV with specific vars

This is to prepare for the elimination of the BUILDENV variable.
Set EXE_EXT explicitly for cms-test.pl

This is in anticipation of removing BUILDENV everywhere.
Remove BUILDENV after configure.mk migration

All of the {GNU,BSD}makefiles now include configure.mk, rendering BUILDENV
obsolete.
Remove BUILDENV from Makefile.fips
Explicitly set EXCL_OBJ env var within ARX command