MFC r312213,r313713:

MFC r312213,r313713:

r312213:

Turn COMPILER_VERSION/COMPILER_TYPE make check into a compile-time check
of the clang version

This works around breakage on ^/stable/10 when running installworld from
a ^/stable/10 host where the test wouldn't be compiled on the first
go-around and would be missing when make installworld is run.

PR:		208703

r313713:

Handle clang 4.x+ with the compile-time exception added in r312213

It also fails the assertions noted in bug 208703

PR:	208703
PR:	217084

git-svn-id: svn://svn.freebsd.org/base/stable/10@314023 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f