Stop using the non-uapi <linux/err.h> header file.

We only need it for MAX_ERRNO, and it's time we had somewhere to put
the little assembler utility macros we've been putting off writing.

Change-Id: I9354d2e0dc47c689296a34b5b229fc9ba75f1a83
diff --git a/libc/arch-arm/bionic/syscall.S b/libc/arch-arm/bionic/syscall.S
index 510d298..a622b58 100644
--- a/libc/arch-arm/bionic/syscall.S
+++ b/libc/arch-arm/bionic/syscall.S
@@ -26,8 +26,7 @@
  * SUCH DAMAGE.
  */
 
-#include <linux/err.h>
-#include <machine/asm.h>
+#include <private/bionic_asm.h>
 
 ENTRY(syscall)
     mov     ip, sp