[ThinLTO] Use decimal suffix for promoted values to match demanglers

Summary:
Demanglers such as libiberty know how to strip suffixes of the form
\.[a-zA-Z]+\.\d+, but our current promoted value suffixes are
.llvm.${modulehash}, where the module hash is in hex. Change the
module hash to decimal to allow demanglers to handle this.

Reviewers: danielcdh

Subscribers: llvm-commits, inglorion

Differential Revision: https://reviews.llvm.org/D38405

llvm-svn: 314527