Update it for the libcall change in #126880.

Some targets (e.g. PPC and Hexagon) already did this. I think it's best
to do this consistently so that frontend authors don't run into
inconsistent results when they emit `naked` functions. For example, in
Zig, we had to change our emit code to also set `frame-pointer=none` to
get reliable results across targets.

Note: I don't have commit access.

This reverts commit 2501ae58e3bb9a70d279a56d7b3a0ed70a8a852c.

Reverted due to various buildbot failures.

PR #66334 tried to renumber slot indexes before register allocation, but
the numbering was still affected by list entries for instructions which
had been erased. Fix this to make the register allocator's live range
length heuristics even less dependent on the history of how instructions
have been added to and removed from SlotIndexes's maps.

Optimize "Rx * imm" for specific immediates to
([IXH32|IXW32|IXD32] (LSLI Rx, shift), Rx).

Reviewed By: zixuan-wu

Differential Revision: https://reviews.llvm.org/D154768

These tests will be optimized with IXH32/IXW32/IXD32
in the future.

Reviewed By: zixuan-wu

Differential Revision: https://reviews.llvm.org/D154332

Reviewed By: zixuan-wu

Differential Revision: https://reviews.llvm.org/D154768