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-x86_64/bionic/syscall.S b/libc/arch-x86_64/bionic/syscall.S
index 6b84ba4..a98a436 100644
--- a/libc/arch-x86_64/bionic/syscall.S
+++ b/libc/arch-x86_64/bionic/syscall.S
@@ -38,9 +38,7 @@
  *   %r9: arg5
  */
 
-#include <asm/unistd.h>
-#include <linux/err.h>
-#include <machine/asm.h>
+#include <private/bionic_asm.h>
 
 ENTRY(syscall)
     # All arguments are passed via registers.
@@ -63,3 +61,4 @@
     orq     $-1, %rax
 1:
     ret
+END(syscall)