[PATCH 1/4] configure: provide llvm_as helper variable

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

Run the file through target specific preprocessing stage.
Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

Removes most overrides
Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

These 4 look ok to me.

I went and tested atomic_min/atomic_max in the CTS/atomics group for
possible regressions on my RX580, the rest was just reviewed by eye
and compile tested. If you think there's anything else that warrants
testing let me know, but I figured that was the most important thing
to check in this series.

--Aaron