[infra] Ignore wheezy sysroot for Linux ARM cross-builds

tools/gn.py

Index: tools/gn.py
diff --git a/tools/gn.py b/tools/gn.py
index 53f9993b48ff47ddfbee6c399d327ef4fed945f3..71823e0555a2624978a0d9c9373931a42d058116 100755
--- a/tools/gn.py
+++ b/tools/gn.py
@@ -141,6 +141,7 @@ def ToGnArgs(args, mode, arch, target_os):
   gn_args['dart_target_arch'] = arch
   gn_args['target_cpu'] = TargetCpuForArch(arch, target_os)
   gn_args['host_cpu'] = HostCpuForArch(arch)
+  crossbuild = gn_args['target_cpu'] != gn_args['host_cpu']
 
   # See: runtime/observatory/BUILD.gn.
   # This allows the standalone build of the observatory to fall back on
@@ -197,7 +198,7 @@ def ToGnArgs(args, mode, arch, target_os):
   gn_args['is_tsan'] = args.tsan and gn_args['is_clang']
 
   # Setup the user-defined sysroot.
-  if gn_args['target_os'] == 'linux' and args.wheezy:
+  if gn_args['target_os'] == 'linux' and args.wheezy and not crossbuild:
     gn_args['dart_use_wheezy_sysroot'] = True
   else:
     sysroot = TargetSysroot(args)