[CIR] clang-tidy CIRGenModule.cpp (#1428)

Run clang-tidy on `clang/lib/CIR/CodeGen/CIRGenModule.cpp`. Accept all
of the recommended fixes, except for one suggestion to use
`std::any_of`. The vast majority of the changes had to do with the case
of identifiers, changing variables and parameters from `VarName` to
`varName`.

Author: dkolsen-pgi