Run misc-use-internal-linkage check over clang-tidy code.
Also fixed a couple of other clang-tidy warnings.
Apart from issues in header files, all '.cpp' in
`clang-tools-extra/clang-tidy` must be clang-tidy clear now.
Detects when a variable is both incremented/decremented and referenced inside a
complex condition and suggests moving them outside to avoid ambiguity in the
variable's value.
Reviewed By: xgupta
Differential Revision: https://reviews.llvm.org/D149015
