build: fix arm64 cross-compilation

Commit 938212f added -msign-return-address=all to _all_ cflags but that
is wrong when cross-compiling, it should only be added to the target's
cflags.

Fixes: nodejs#42888

configure.py

@@ -1247,9 +1247,7 @@ def configure_node(o):
 
   o['variables']['want_separate_host_toolset'] = int(cross_compiling)
 
-  # Enable branch protection for arm64
   if target_arch == 'arm64':
-    o['cflags']+=['-msign-return-address=all']
     o['variables']['arm_fpu'] = options.arm_fpu or 'neon'
 
   if options.node_snapshot_main is not None:

node.gyp

@@ -109,6 +109,9 @@
     },
 
     'conditions': [
+      ['target_arch=="arm64"', {
+        'cflags': ['-msign-return-address=all'],  # Pointer authentication.
+      }],
       ['OS=="aix"', {
         'ldflags': [
           '-Wl,-bnoerrmsg',