Adds deprecation messages for MIPS cross-builds

tools/gn.py

Index: tools/gn.py
diff --git a/tools/gn.py b/tools/gn.py
index f0c1d91460c0966593026e2e0ba24b16df52e6d1..3a8a69df77b4667af9f48a3d0cac6872e382d497 100755
--- a/tools/gn.py
+++ b/tools/gn.py
@@ -144,6 +144,14 @@ def ToGnArgs(args, mode, arch, target_os):
   else:
     gn_args['target_os'] = target_os
 
+  if arch.startswith('mips'):
+    bold  = '\033[1m'
+    reset = '\033[0m'
+    print(bold + "Warning: MIPS architectures are unlikely to be supported in "
+          "upcoming releases. Please consider using another architecture "
+          "and/or file an issue explaining your specific use of and need for "
+          "MIPS support." + reset)
+
   gn_args['dart_target_arch'] = arch
   gn_args['target_cpu'] = TargetCpuForArch(arch, target_os)
   gn_args['host_cpu'] = HostCpuForArch(arch)
@@ -244,7 +252,7 @@ def ProcessOsOption(os_name):
 
 def ProcessOptions(args):
   if args.arch == 'all':
-    args.arch = 'ia32,x64,simarm,simarm64,simmips,simdbc64'
+    args.arch = 'ia32,x64,simarm,simarm64,simdbc64'
   if args.mode == 'all':
     args.mode = 'debug,release,product'
   if args.os == 'all':