platform.in: change %__nprocs definition to use %getncpus instead of nproc(1)

Both use sched_getaffinity(2), but %getncpus is built-in and saves fork
and execve.

Suggested-by: Dmitry V. Levin <ldv@altlinux.org>

platform.in

@@ -240,7 +240,7 @@
 # Make
 %_make_bin make
 
-%__nprocs	%(N=`nproc`; [ "$N" -gt 0 ] 2>/dev/null && echo "$N" || echo 1)
+%__nprocs	%getncpus
 %_smp_mflags	-j${NPROCS:-%__nprocs}
 %make_build	%_make_bin %_smp_mflags