[Clang][CodeGen] set alias linkage on QualType
It seems that CodeGen was always using ExternalLinkage when emitting a
GlobalDecl with attribute((alias)). This leads to symbol
redefinitions (ODR) that cause failures at link time for static aliases.
This is readily attempting to link an ARM (32b) allyesconfig Linux
kernel built with Clang.
Reviewers: rsmith, aaron.ballman, erichkeane
Reviewed By: aaron.ballman
Subscribers: javed.absar, kristof.beyls, cfe-commits, srhines, ihalip, nathanchance
Differential Revision: https://reviews.llvm.org/D66492