Adds a flag to the gn script to build with -fstack-protector (flutter#34257)

Author: zanderso

DEPS

@@ -111,7 +111,7 @@ allowed_hosts = [
 ]
 
 deps = {
-  'src': 'https://github.com/flutter/buildroot.git' + '@' + '87d5dcb98983da54257f6f39d3beee2989cb0e47',
+  'src': 'https://github.com/flutter/buildroot.git' + '@' + 'e27b16edf1fd54c358cc9499aa02297100375354',
 
    # Fuchsia compatibility
    #

tools/gn

@@ -495,6 +495,9 @@ def to_gn_args(args):
   if args.ubsan:
     gn_args['is_ubsan'] = True
 
+  if args.fstack_protector:
+    gn_args['use_fstack_protector'] = True
+
   if args.enable_vulkan_validation_layers:
     if args.target_os != 'fuchsia':
       print(
@@ -860,6 +863,13 @@ def parse_args(args):
   parser.add_argument('--tsan', default=False, action='store_true')
   parser.add_argument('--ubsan', default=False, action='store_true')
 
+  parser.add_argument(
+      '--fstack-protector',
+      default=False,
+      action='store_true',
+      help='Whether the -fstack-protector flag should be passed unconditionally.'
+  )
+
   parser.add_argument(
       '--trace-gn',
       default=False,