Option parsing: support case-insensitive option matching.

Re-submitting r189416 with fix for Windows build on where strcasecmp is not defined.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189501 91177308-0d34-0410-b5e6-96231b3b80d8
[cmake] Created an aggregate doxygen target for generating doxygen documentation for llvm/all subprojects. Renamed llvm's doxygen generation command to doxygen-llvm.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189506 91177308-0d34-0410-b5e6-96231b3b80d8
[doxygen] Added support for doxygen external search.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189507 91177308-0d34-0410-b5e6-96231b3b80d8
r189495: Pull out some debug logic into a function for legibility

Code review feedback from Eric Christopher.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189512 91177308-0d34-0410-b5e6-96231b3b80d8
Period.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189513 91177308-0d34-0410-b5e6-96231b3b80d8