Fixed ndk-gdb-py.cmd on SHELL

Set SHELL as env. var. instead of passing it to python.exe which
can't understand it.

See b.android.com/63054

Change-Id: I3c751237b1a929543a881321fb2657850b4f4eb8
diff --git a/ndk-gdb-py.cmd b/ndk-gdb-py.cmd
index 07065e4..265ca55 100644
--- a/ndk-gdb-py.cmd
+++ b/ndk-gdb-py.cmd
@@ -2,5 +2,8 @@
 rem This is a Windows cmd.exe script used to invoke the NDK-specific Python executable
 call "%~dp0find-win-host.cmd" NDK_WIN_HOST
 if ERRORLEVEL 1 (exit /b 1)
+setlocal
 set NDK_ROOT=%~dp0
-"%NDK_ROOT%prebuilt/%NDK_WIN_HOST%/bin/python.exe" -u "%~dp0ndk-gdb.py" SHELL=cmd %*
+set SHELL=cmd
+"%NDK_ROOT%prebuilt/%NDK_WIN_HOST%/bin/python.exe" -u "%~dp0ndk-gdb.py" %*
+endlocal