Fix autoninja.bat to not swallow ^^ sequences

Ninja uses the '^' character to indicate that ninja should build the
targets that are generated from the specified file, rather than
building the specified file. On Windows '^^' is needed because '^' is
the line continuation character. However autoninja.bat complicates
things because the multiple levels of batch files successfully swallow
pairs of '^' characters.

By adding quotes around %* in autoninja.bat it becomes possible to
invoke autoninja.bat normally. That is, this works:

    autoninja -C out\debug_component ..\..\base\win\enum_variant.cc^^

It can be convenient to have a ninja.bat file which starts goma and lets
users keep typing the same build commands. However even with this fix
the previously recommended ninja.bat file requires four '^' characters.
If that is too much then the new recommended ninja.bat is to copy
autoninja.bat and modify as needed, perhaps like this:

    @echo off
    call python c:\goma\goma-win64\goma_ctl.py ensure_start >nul
    FOR /f "usebackq tokens=*" %%a in (`python c:\src\depot_tools\autoninja.py "%*"`) do echo %%a & %%a

BUG=758725

Change-Id: I648cf42675af2f946be7aa4033956b015d953829
Reviewed-on: https://chromium-review.googlesource.com/651826
Reviewed-by: Sébastien Marchand <sebmarchand@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>

autoninja.bat

@@ -5,5 +5,5 @@
 
 REM Execute whatever is printed by autoninja.py.
 REM Also print it to reassure that the right settings are being used.
-FOR /f "usebackq tokens=*" %%a in (`python %~dp0autoninja.py %*`) do echo %%a & %%a
+FOR /f "usebackq tokens=*" %%a in (`python %~dp0autoninja.py "%*"`) do echo %%a & %%a