Add cfi directives for arm64 assembler.

Fix syscall generator to add cfi directives and add the directives
for all arm64 assembler.

Bug: 15138290
Change-Id: I7f0e4a16c141ac624e5276917a3a1ed45778e057
diff --git a/libc/arch-arm64/bionic/syscall.S b/libc/arch-arm64/bionic/syscall.S
index e5be1d5..42e8883 100644
--- a/libc/arch-arm64/bionic/syscall.S
+++ b/libc/arch-arm64/bionic/syscall.S
@@ -31,11 +31,11 @@
 ENTRY(syscall)
     /* create AAPCS frame pointer */
     stp     x29, x30, [sp, #-16]!
+    .cfi_def_cfa_offset 16
+    .cfi_rel_offset x29, 0
+    .cfi_rel_offset x30, 8
     mov     x29,  sp
 
-    /* store x8 */
-    str     x8,       [sp, #-16]!
-
     /* Move syscall No. from x0 to x8 */
     mov     x8, x0
     /* Move syscall parameters from x1 thru x6 to x0 thru x5 */
@@ -47,9 +47,10 @@
     mov     x5, x6
     svc     #0
 
-    /* restore x8 */
-    ldr     x8,       [sp], #16
     ldp     x29, x30, [sp], #16
+    .cfi_def_cfa_offset 0
+    .cfi_restore x29
+    .cfi_restore x30
 
     /* check if syscall returned successfully */
     cmn     x0, #(MAX_ERRNO + 1)