[clang-scan-deps] do not skip empty #if/#elif in the minimizer to avoid missing ...

[clang-scan-deps] do not skip empty #if/#elif in the minimizer to avoid missing `__has_include` dependencies

This patch makes the minimizer more conservative to avoid missing dependency files that are brought in by __has_include
PP expressions that occur in a condition of an #if/#elif that was previously skipped. The __has_include PP expressions
can be used in an #if/#elif either directly, or through macro expansion, so we can't detect them at the time of minimization.

Differential Revision: https://reviews.llvm.org/D70936