[GN] Add a --ios-cpu flag to build an iOS armv7 capable Flutter engine. (#4063)

DEPS

@@ -113,7 +113,7 @@ allowed_hosts = [
 ]
 
 deps = {
-  'src': 'https://github.com/flutter/buildroot.git' + '@' + '0d01e11fdf70dc1ee14e3bd1e7219b4ac84d1524',
+  'src': 'https://github.com/flutter/buildroot.git' + '@' + '8280a05606fcf91970aa2d480154894d477ab358',
 
    # Fuchsia compatibility
    #

tools/gn

@@ -27,6 +27,9 @@ def get_out_dir(args):
     if args.android_cpu != 'arm':
         target_dir.append(args.android_cpu)
 
+    if args.ios_cpu != 'arm64':
+        target_dir.append(args.ios_cpu)
+
     if args.enable_vulkan:
         target_dir.append('vulkan')
 
@@ -102,7 +105,7 @@ def to_gn_args(args):
         if args.simulator:
             gn_args['target_cpu'] = 'x64'
         else:
-            gn_args['target_cpu'] = 'arm64'
+            gn_args['target_cpu'] = args.ios_cpu
     else:
         # Building host artifacts
         gn_args['target_cpu'] = 'x64'
@@ -161,8 +164,6 @@ def to_gn_args(args):
       gn_args['use_goma'] = False
       gn_args['goma_dir'] = None
 
-    gn_args['use_glfw'] = args.use_glfw
-
     if args.enable_vulkan:
       # Enable vulkan in the Flutter shell.
       gn_args['shell_enable_vulkan'] = True
@@ -188,6 +189,7 @@ def parse_args(args):
   parser.add_argument('--android', dest='target_os', action='store_const', const='android')
   parser.add_argument('--android-cpu', type=str, choices=['arm', 'x64', 'x86', 'arm64'], default='arm')
   parser.add_argument('--ios', dest='target_os', action='store_const', const='ios')
+  parser.add_argument('--ios-cpu', type=str, choices=['arm', 'arm64'], default='arm64')
   parser.add_argument('--simulator', action='store_true', default=False)
 
   parser.add_argument('--goma', default=True, action='store_true')