Fix link error on Linux/musl.

get_nprocs() is a GNU convenience function equivalent to POSIX2008
sysconf(_SC_NPROCESSORS_ONLN); the latter should be available in unistd.h
on any current *nix. (OS X supports this call since 10.5, and FreeBSD
currently supports it. But this commit does not change FreeBSD or OS X
versions.)

driver/others/init.c

@@ -865,7 +865,7 @@ void gotoblas_set_affinity2(int threads) {};
 
 void gotoblas_affinity_reschedule(void) {};
 
-int get_num_procs(void) { return get_nprocs(); }
+int get_num_procs(void) { return sysconf(_SC_NPROCESSORS_ONLN); }
 
 int get_num_nodes(void) { return 1; }