libdrm: unbreak musl build (PATH_MAX is declared in limits.h).

srcpkgs/libdrm/patches/musl.patch

@@ -0,0 +1,10 @@
+--- xf86drm.c.orig	2015-09-17 07:47:33.627138291 +0200
++++ xf86drm.c	2015-09-17 07:47:51.209322782 +0200
+@@ -46,6 +46,7 @@
+ #include <errno.h>
+ #include <signal.h>
+ #include <time.h>
++#include <limits.h>	/* PATH_MAX */
+ #include <sys/types.h>
+ #include <sys/stat.h>
+ #define stat_t struct stat