Backport of this upstream commit, with ports/ readded to the path.

commit b8528e771c0f31ebb8ac2470e2cf7ee9a50693e2
Author: Szabolcs Nagy <nsz@port70.net>
Date:   Thu Jul 9 09:53:30 2015 +0100

    [AArch64][BZ 18648] change greg_t definition in ucontext.h
    
    This is an ABI breaking change, but
    
    	typedef int greg_t;
    
    is not a useful definition on aarch64.
    
    greg_t is usually used for defining gregset_t which is used
    in mcontext_t.  The general registers in mcontext_t can only
    be accessed by target specific code and on aarch64 greg_t
    is not needed for that so this change is not supposed to break
    existing code, just fix the definition.
    
    	[BZ #18648]
    	* sysdeps/unix/sysv/linux/aarch64/sys/ucontext.h (greg_t): Change the
    	definition to elf_greg_t.
    
    (Added another BZ entry that was missed in the previous commit).

diff --git a/ports/sysdeps/unix/sysv/linux/aarch64/sys/ucontext.h b/ports/sysdeps/unix/sysv/linux/aarch64/sys/ucontext.h
index db7a7c1..e7268ce 100644
--- a/ports/sysdeps/unix/sysv/linux/aarch64/sys/ucontext.h
+++ b/ports/sysdeps/unix/sysv/linux/aarch64/sys/ucontext.h
@@ -29,7 +29,7 @@
    included in <signal.h>.  */
 #include <bits/sigcontext.h>
 
-typedef int greg_t;
+typedef elf_greg_t greg_t;
 
 /* Container for all general registers.  */
 typedef elf_gregset_t gregset_t;