powerpc: Fix __wcschr static build

This patch fix the static build for strftime, which uses __wcschr.
Current powerpc32 implementation defines the __wcschr be an alias to
__wcschr_ppc32 and current implementation misses the correct alias for
static build.

It also changes the default wcschr.c logic so a IFUNC implementation
should just define WCSCHR and undefine the required alias/internal
definitions.