yquake2: fix musl build.

srcpkgs/yquake2/patches/musl.patch

@@ -17,3 +17,13 @@
  void
  printBacktrace(int sig)
  {
+--- src/backends/unix/system.c
++++ src/backends/unix/system.c
+@@ -34,6 +34,7 @@
+ #include <time.h>
+ #include <unistd.h>
+ #include <sys/stat.h>
++#include <sys/select.h>
+ 
+ #ifdef __APPLE__
+ #include <mach/clock.h>