Use CFN_BUILT_IN_CLRSB instead of BUILT_IN_CLRSB in switch.

Use CFN_BUILT_IN_CLRSB instead of BUILT_IN_CLRSB in switch.

This patch replaces the use of BUILT_IN_CLRSB with CFN_BUILT_IN_CLRSB
in my recent patch to tree-ssa-phiopt.c.  Both of these have identical
values, so there's no change in behavior, but consistent use of the same
enumeration avoids warnings when using clang (or static analysis tools).

2021-08-06  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* tree-ssa-phiopt.c (cond_removal_in_builtin_zero_pattern): Use
	CFN_BUILT_IN_CLRSB* instead of BUILT_IN_CLRSB* for consistency.