MFC 278582:

MFC 278582:
MFi386:
When building some of the boot loaders with clang, and DEBUG_FLAGS or
CFLAGS having '-g' in it, clang outputs several assembly directives that
are too new for our version of binutils.

Therefore, assemble the resulting .s files with clang instead.  A more
general solution can be implemented when a GNU as-compatible driver for
clang's integrated assembler appears.

git-svn-id: svn://svn.freebsd.org/base/stable/10@290124 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f