[Modules] Sink all the DEBUG_TYPE defines for InstCombine out of the
header files and into the cpp files.

These files will require more touches as the header files actually use
DEBUG(). Eventually, I'll have to introduce a matched #define and #undef
of DEBUG_TYPE for the header files, but that comes as step N of many to
clean all of this up.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206777 91177308-0d34-0410-b5e6-96231b3b80d8