[DebugInfo] Rename EmitDebugThreadLocal back to EmitDebugValue. NFC

This reverts r294500. DwarfCompileUnit::addAddressExpr uses DIEExpr
for PCOffset. In that case the expression is unrelated to thread locals
and so emitting a value of the DIEExpr does not have to always mean
emit-debug-thread-local.

llvm-svn: 347744