Refactor the x86 CPU name logic in the driver and pass -march and -mcpu
flag information down from the Clang driver into the Gold linker plugin
for LTO. This allows specifying -march on the linker commandline and
should hopefully have it pass all the way through to the LTO optimizer.
Fixes PR14697.
Pull in r175919 from upstream clang trunk:
Driver: Pass down the -march setting down to -cc1as on x86 too.
The assembler historically didn't make use of any target features, but this has
changed when support for old CPUs that don't support long nops was added.
This should fix the long nops that still occurred in crt*.o, and
possibly other object files, if the system was compiled for a CPU that
does not support those, such as Geode.
Note that gcc on i386 also does not pass through any -march, -mcpu or
-mtune setting to gas, but this has not caused any trouble yet, because
gas defaults to i386.
Reported by: lev
MFC after: 1 week
2d97b320fb