CodeGen: Avoid multiple strlen calls

Use a StringRef to hold our section prefix.  This avoids multiple calls
to strlen.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211602 91177308-0d34-0410-b5e6-96231b3b80d8
Resubmit commit r211533

"Fix PR20056: Implement pseudo LDR <reg>, =<literal/label> for AArch64"
Missed files are added in this commit.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211605 91177308-0d34-0410-b5e6-96231b3b80d8