ThinLTO: Fix inline assembly references to static functions with CFI
Create an internal alias with the original name for static functions
that are renamed in promoteInternals to avoid breaking inline
assembly references to them.
This relands commit 4474958d3a97dede2caa0920f7c4a4dc7aac57d3
with a fix to a use-of-uninitialized-value error that tripped
Reviewed By: nickdesaulniers, pcc
Differential Revision: https://reviews.llvm.org/D104058