[analyzer] Refer to macro names in diagnostics for macros representing a literal

When a macro expending to a literal is used in a comparison, use the macro name
in the diagnostic rather than the literal. This improves readability of path
notes.

Added tests for various macro literals that could occur. Only BOOl, Int, and
NULL tests have changed behavior with this patch.

Differential Revision: https://reviews.llvm.org/D27726

llvm-svn: 289884