Pull in r329557 from upstream lld trunk (by George Rimar):

[ELF] - Allow LLD to produce file symbols.

This is for PR36716 and
this enables emitting STT_FILE symbols.

Output size affect is minor:
lld binary size changes from 52,883,408 to 52,949,400
clang binary size changes from 83,136,456 to 83,219,600

Differential revision: https://reviews.llvm.org/D45261

This fixes a regression in lld that made it stop emitting STT_FILE
symbols, which ctfmerge relies upon to uniquify function table entries
that reference STB_LOCAL symbols. Consequently, ctfmerge stopped
emitting entries for static functions into the function table, and
dtrace no longer gets type info for them.

Approved by: re (kib)
Reported by: markj
PR: 230444
MFC after: 3 days