[ValueTracking] Add logic for `fshl/fshr(A, B, C) != 0` if `A == B && A ! = 0`

Having `A == B` is quite common for rotate patterns.

Alive2 Links:
    - https://alive2.llvm.org/ce/z/mPXi9c
    - https://alive2.llvm.org/ce/z/UfDHoI

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D149372