I'll commit this in two parts:
stand: push LIBC_SRC up into defs.mk
Other parts of stand/ that don't use libsa will need to grab bits from libc shortly. Push LIBC_SRC up to defs.mk in advance of this so that they can use it, and rename it to LIBCSRC to match the convention of the rest of the *SRC variables in this file.
(SECOND COMMIT BELOW)
stand: fix build with xtoolchain-llvm90
ufsread.c grows a dependency on __ashldi3 with llvm90. This exposes itself primarily in gptboot and i386/boot2.
For gptboot, just start pulling in ashldi3.c ashrdi3.c lshrdi3.c into libsa for all archs except riscv[*] as the number of archs requiring one or more of them keeps growing.
For boot2, reach into libc/quad and grab it.
Prototypes are added to the two quad.h used during the stand build to appease -Wmissing-prototypes where that crops up. Future work will try to eliminate the duplicate quad.h...
libsa/quad.h no longer compensates for GNUC < 2. It's been long enough that this isn't relevant anymore, and this puts libsa/quad.h closer in line to libc/quad/quad.h.
- riscv build doesn't currently like __ashldi3 and it doesn't really need it, so this one's left out for now.