Enable building LTO on WIN32.

Enable building the LTO library (.lib and.dll) and llvm-lto.exe on Windows with
MSVC and Mingw as well as re-enabling the associated test.

Patch by Greg Bedwell!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191823 91177308-0d34-0410-b5e6-96231b3b80d8
Add Support For .bss Named Section Directive For Darwin Targets.

Patch by Nicholas White.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191824 91177308-0d34-0410-b5e6-96231b3b80d8
Add a -exported-symbol option to llvm-lto.

Patch by Tom Roeder.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191825 91177308-0d34-0410-b5e6-96231b3b80d8
Don't layout items in a list in columns. That requires changing every
line just to add or remove a single element. What I wouldn't give to
have clang-format here an be able to format this more densely without
caring...

Re-group and sort the entries while here to make the whole thing more
clear.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191828 91177308-0d34-0410-b5e6-96231b3b80d8
Fix option parsing in the gold plugin.

This was broken when options were moved up in r191680. No test because this is
specific LLVMgold.so/libLTO.so.

Patch by Tom Roeder!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191829 91177308-0d34-0410-b5e6-96231b3b80d8
Disable this test on Win32 for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191830 91177308-0d34-0410-b5e6-96231b3b80d8
Add test I forgot to git add in r191824.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191831 91177308-0d34-0410-b5e6-96231b3b80d8