Backport fix for evaluating %pcrel_lo against global and weak symbols

[asb]

Bugzilla Link	44631
Resolution	FIXED
Resolved on	Jan 23, 2020 09:31
Version	10.0
OS	All
Blocks	#43900

Extended Description

https://reviews.llvm.org/D73211 is an important fix to a regression that affects building FreeRTOS, FreeBSD, and possibly other software stacks using LLVM.

Please apply
https://reviews.llvm.org/D73211 (3f5976c) and the follow-up lld test fix ddfe875 to the release branch.

[asb]

assigned to @zmodem

[asb]

I've confirmed these patches apply cleanly to the release branch.

[zmodem]

Cherry-picked in 8634a82 and a3982a5. Thanks!