Correctly handle an ELF symbol defined with "a = b + expr".

We were marking the symbol as absolute instead of computing b's offset + the
expression value.

This fixes pr19126.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203962 91177308-0d34-0410-b5e6-96231b3b80d8
MCContext: Remove redundant assignment

The member variable is not initialized in the ctor so it's already
empty. No need to empty it again.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203963 91177308-0d34-0410-b5e6-96231b3b80d8
MCDwarf: Initialize MCLineTableHeader::Label

This sometimes remains null into MCLineTableHeader::Emit where we
conditionally construct a label if one isn't provided for us. We need it
to remain null (rather than just always constructing the label) so we
can identify unused line tables... which is a bit weird and maybe we can
do away with that logic one day (& on that day we can always construct
the label up-front and just have compilation units query the line table
for its label, etc)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203967 91177308-0d34-0410-b5e6-96231b3b80d8
Remove the -generate-dwarf-cu-ranges flag.
Rewrite a couple of testcases to cover areas that would be normally
by turning it on into testcases that will follow the logic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203968 91177308-0d34-0410-b5e6-96231b3b80d8
If we see that we're emitting code for a function that doesn't have
any lexical scopes then go ahead and turn on DW_AT_ranges for the
compile unit since we would be claiming to describe in the CU
a range for which we don't have information in the CU otherwise.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203969 91177308-0d34-0410-b5e6-96231b3b80d8