Support omitting the space after -C

Nina supports -C out/Default and -Cout/Default to specify the build
directory so autoninja should also. This change adds that support.

Bug: 890744
Change-Id: I5e824242ed4b333ac99f1ee9a649ffcfa03a812e
Reviewed-on: https://chromium-review.googlesource.com/c/1257586
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>

autoninja.py

@@ -38,6 +38,9 @@ for index, arg in enumerate(input_args[1:]):
   if arg == '-C':
     # + 1 to get the next argument and +1 because we trimmed off input_args[0]
     output_dir = input_args[index + 2]
+  elif arg.startswith('-C'):
+    # Support -Cout/Default
+    output_dir = arg[2:]
 
 use_goma = False
 try: