[clang] Fix time profile in "isIntegerConstantExpr"

The time profiler in `Expr::isIntegerConstantExpr` used to
call `Loc->printToString`, it was inconsistent with other time
profiles in the file and caused segfaults if `Loc` was `nullptr`.

Fixes https://github.com/llvm/llvm-project/issues/58551

Reviewed By: dyung, jloser

Differential Revision: https://reviews.llvm.org/D136549