Take LINKER_FREEBSD_VERSION from numerical field after dash

Summary:
With COMPILER_FREEBSD_VERSION, we use a numeric value that we bump each
time we make a change that requires re-bootstrapping, but with the
linker variant, we instead take the entire part after "FreeBSD", as in
this example version output:

LLD 9.0.1 (FreeBSD c1a0a213378a458fbea1a5c77b315c7dce08fd05-1300006) (compatible with GNU linkers)

E.g., LINKER_FREEBSD_VERSION is currently being set to
"c1a0a213378a458fbea1a5c77b315c7dce08fd05-1300006".  This means that
*any* new upstream lld version will cause re-bootstrapping.

We should only look at the numerical field we append after a dash
instead.  This review attempts to make it so.

The only thing I am not happy about is the post-processing of awk output
in Makefile.inc1.  I notice that our awk does not have gensub(), so it
can't substitute a numbered sub-regex with \1, \2, etc.  Suggestions
welcome. :)

MFC after:	1 week
Differential Revision: https://reviews.freebsd.org/D23691

1 files changed, 2 insertions, 1 deletions

diff --git a/Makefile.inc1 b/Makefile.inc1
index 4f7aaae6d654..0139ca875262 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -272,9 +272,10 @@ WANT_LINKER_TYPE=
     !make(test-system-compiler)
 .if ${WANT_LINKER_TYPE} == "lld"
 WANT_LINKER_FREEBSD_VERSION_FILE= lib/clang/include/VCSVersion.inc
-WANT_LINKER_FREEBSD_VERSION!= \
+_WANT_LINKER_FREEBSD_VERSION!= \
 	awk '$$2 == "LLD_REVISION" {gsub(/"/, "", $$3); print $$3}' \
 	${SRCDIR}/${WANT_LINKER_FREEBSD_VERSION_FILE} || echo unknown
+WANT_LINKER_FREEBSD_VERSION=${_WANT_LINKER_FREEBSD_VERSION:C/.*-(.*)/\1/}
 WANT_LINKER_VERSION_FILE= lib/clang/include/lld/Common/Version.inc
 WANT_LINKER_VERSION!= \
 	awk '$$2 == "LLD_VERSION" {split($$3, a, "."); print a[1] * 10000 + a[2] * 100 + a[3]}' \