[CodeGen] Require a name for a block addr target

[CodeGen] Require a name for a block addr target

Summary:
A block address may be used in inline assembly. In which case it
requires a name so that the asm parser has something to parse. Creating
a name for every block address is a large hammer, but is necessary
because at the point when a temp symbol is created we don't necessarily
know if it's used in inline asm. This ensures that it exists regardless.

Reviewers: nickdesaulniers, craig.topper

Subscribers: nathanchance, javed.absar, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65352

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@368478 91177308-0d34-0410-b5e6-96231b3b80d8