Log message:
*: Remove many GCC_REQD for particularly old GCCs

In many cases the reasoning is poorly documented, or the reasoning
for setting GCC_REQD is to work around a compiler bug. Practically
a c99 compiler is now required for bootstrap (in at least several
dependencies) so we can entirely rule out GCC versions before 3.0.

Log message:
biology: Replace RMD160 checksums with BLAKE2s checksums

All checksums have been double-checked against existing RMD160 and
SHA512 hashes

Log message:
biology: Remove SHA1 hashes for distfiles

Log message:
Add SHA512 digests for distfiles for biology category.

Existing SHA1 digests verified, all found to be the same on the
machine holding the existing distfiles (morden).  Existing SHA1
digests retained for now as an audit trail.

Log message:
Remove xextproto/buildlink3.mk in most cases where it occurs with
libXext/buildlink3.mk, now that it is included there.
Leave the places where its API version is set or variables from it
are used directly (about 3 packages).

Log message:
"user-destdir" is default these days

Log message:
Remove RCS directory, or may failed to patch due to locked under RCS.

Log message:
user-destdir support

Log message:
Remove @dirrm entries from PLISTs

Log message:
Modular Xorg support.