DwarfAccelTable: Store the string symbol in the accelerator table to avoid duplicate lookup.

This also avoids the need for subtly side-effecting calls to manifest
strings in the string table at the point where items are added to the
accelerator tables.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207281 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Fix function name printing in LowerCall

v2: Check both ExternalSymbol and GlobalAddress

Patch by: Jan Vesely <jan.vesely@rutgers.edu>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207282 91177308-0d34-0410-b5e6-96231b3b80d8