[libunwind] Fix build error because of wrong register size

This patch should fix an libunwind build failure that happens on
Chromium's Android bots:

#165066 (comment)

The issue is that we're using the `wzr` register to move the value 0 in
x1, but this is the 32-bit register. We should be using the 64-bit
version, `xzr` instead.

Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>

Author: medismailben

libunwind/src/UnwindLevel1.c

@@ -82,7 +82,7 @@
     void *shstkRegContext = __libunwind_shstk_get_registers((cursor));         \
     void *shstkJumpAddress = __libunwind_shstk_get_jump_target();              \
     __asm__ volatile("mov x0, %0\n\t"                                          \
-                     "mov x1, wzr\n\t"                                         \
+                     "mov x1, xzr\n\t"                                         \
                      "br %1\n\t"                                               \
                      :                                                         \
                      : "r"(shstkRegContext), "r"(shstkJumpAddress)             \