Enable clang and host_os when generating ninja-ios.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index cf259c31818fd593dc1bd2f313690a3916e71927..32a6ef3d498a1b7b5e2c33f216b4c5c505e69a37 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -1510,6 +1510,14 @@
           # iOS uses a whitelist to filter resources.
           '-w', '<(DEPTH)/build/ios/grit_whitelist.txt'
         ],
+
+        # Enable clang and host builds when generating with ninja-ios.
+        'conditions': [
+          ['"<(GENERATOR)"=="ninja"', {
+            'clang%': 1,
+            'host_os%': "mac",
+          }]
+        ],
       }],
       ['enable_extensions==1', {
         'grit_defines': ['-D', 'enable_extensions'],