Treat -g1 as -gline-tables-only

-g1 on gcc (and also IBM's xlc) are documented to be very similar to
-gline-tables-only. Our -gline-tables-only might still be more verbose than -g1
on other compilers, but currently we treat -g1 as -g, and so we're producing
much more debug info at -g1 than everybody else. Treating -g1 as
-gline-tables-only brings us much closer to what everyone else is doing.

For more information, see the discussion on
http://lists.cs.uiuc.edu/pipermail/cfe-dev/2014-October/039649.html

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@220311 91177308-0d34-0410-b5e6-96231b3b80d8
Follow-up commit to r211657 which introduced these macros, but not for MSVC. This turns out to break our freestanding tests on Windows when compiling in MSVC-compatible mode. It was decided (http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20141020/116942.html is the start of the thread) to support this as part of Clang's interface on all platforms.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@220312 91177308-0d34-0410-b5e6-96231b3b80d8
Removing unused variable (assigned into, but never read from); NFC.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@220313 91177308-0d34-0410-b5e6-96231b3b80d8