Analysis: move declaration of variables to a more suitable location

This moves 2 variable declarations from `llvm/Support/Debug.h` to a more
appropriate home in the headers for `LLVMAnalysis`.  These variables are
defined in `LLVMAnalysis` rather than in `LLVMSupport` and although they
control debugging behavior, the declarations being colocated in the same
library's headers is both easier to locate and aids correctly describing
the library's interfaces.

Reviewed By: rnk, mehdi_amini, aeubanks

Differential Revision: https://reviews.llvm.org/D109396