libcompiler_rt Makefile.inc: include bsd.compiler.mk to fix build

Apparently libgcc_s has always included libcompiler_rt's Makefile.inc
without first including bsd.compiler.mk, even though Makefile.inc used
COMPILER_TYPE already. It looks like we were just lucky that the
expression was not malformed.

PR: 276104
Reported by: Herbert J. Skuhra <herbert@gojira.at>
MFC after: 1 month