[AArch64] Fix libunwind build when using GNU assembler

Use x29 and x30 for fp and lr respectively.

This does not change the code generation with integrated asm
but using x30 and x29 helps compile the code with gnu as. Currently gas
fails to assemble this code with errors as below.

Error: operand X should be an integer register.

Newer versions of binutils should be fixed, but enough exists in the wild
to make this change harmless and worthy.

Patch by Khem Raj.

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@260595 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/UnwindRegistersRestore.S b/src/UnwindRegistersRestore.S
index 3a4ea62..d5ecc6e 100644
--- a/src/UnwindRegistersRestore.S
+++ b/src/UnwindRegistersRestore.S
@@ -282,8 +282,8 @@
   ldp    x22,x23, [x0, #0x0B0]
   ldp    x24,x25, [x0, #0x0C0]
   ldp    x26,x27, [x0, #0x0D0]
-  ldp    x28,fp,  [x0, #0x0E0]
-  ldr    lr,      [x0, #0x100]  // restore pc into lr
+  ldp    x28,x29, [x0, #0x0E0]
+  ldr    x30,     [x0, #0x100]  // restore pc into lr
   ldr    x1,      [x0, #0x0F8]
   mov    sp,x1                  // restore sp
@@ -306,7 +306,7 @@
   ldr    d31,     [x0, #0x208]
   ldp    x0, x1,  [x0, #0x000]  // restore x0,x1
-  ret    lr                     // jump to pc
+  ret    x30                    // jump to pc
 #elif defined(__arm__) && !defined(__APPLE__)
diff --git a/src/UnwindRegistersSave.S b/src/UnwindRegistersSave.S
index f84b711..82becff 100644
--- a/src/UnwindRegistersSave.S
+++ b/src/UnwindRegistersSave.S
@@ -263,11 +263,11 @@
   stp    x22,x23, [x0, #0x0B0]
   stp    x24,x25, [x0, #0x0C0]
   stp    x26,x27, [x0, #0x0D0]
-  stp    x28,fp,  [x0, #0x0E0]
-  str    lr,      [x0, #0x0F0]
+  stp    x28,x29, [x0, #0x0E0]
+  str    x30,     [x0, #0x0F0]
   mov    x1,sp
   str    x1,      [x0, #0x0F8]
-  str    lr,      [x0, #0x100]    // store return address as pc
+  str    x30,     [x0, #0x100]    // store return address as pc
   // skip cpsr
   stp    d0, d1,  [x0, #0x110]
   stp    d2, d3,  [x0, #0x120]