MF10 r352637,r358076: correct Clang and lld version checks

r352637 (mhorne): Allow for compiler versions >= 10
r358076 (dim): Correctly recognize linker versions greater than 10.0.

These routines determine the host compiler and linker version, and caused
attempts to build 12.1-RELEASE on 13-CURRENT to fail after the latter was
updated to Clang 10. We don't guarantee such a build config to work, but
it is used by FreeBSD ports build processes. As a result the fixes from
stable/12 will be included with the next set of advisories, and are being
committed to the branch now to unblock ports builds.

PR: 245973
Reported by: sbruno, antoine
Approved by: so
Errata: EN-20:10.build
Sponsored by: The FreeBSD Foundation