[Bug target/123792] aarch64: stdc_bit_ceil generates inefficient code

[wilco at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123792

--- Comment #3 from Wilco <wilco at gcc dot gnu.org> ---
Note the SUB/CMP issue is due to peepholes only considering adjacent
instructions. -fschedule-insns generates SUBS for the example, but slight
variations like stdc_bit_ceil (n - 1) won't. Making these fusion pairs might be
better.