[fir][NFC] Fix couple of clang-tidy warnings

Fix some clang-tidy wrning in flang/Optimizer/Support and
remove explicit number of inlined elements for SmallVector. This
is mostly to sync with the changes from fir-dev.

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: schweitz

Differential Revision: https://reviews.llvm.org/D111044