Windows: fix MSVC compilations at HEAD

Strip quotes from arg0 in call_python.bat .
This bug was has been there longer, but never got
triggered, because we only quoted arg0 if it
contained spaces, which it most likely never
actually did, or not in this particular case.

After submitting e68c6b5 and 9e8bc63 which fixed
the compilation errors in the former, we started
always quoting argv0 in subprocesses, which
exposed this bug, leading to a corrupt DRIVER_DIR
value in call_python.bat.

Fixes #2402

--
Change-Id: Iab5c00001fc4307f2e23c46c8187f5ef15d83d41
Reviewed-on: https://cr.bazel.build/8436
PiperOrigin-RevId: 145310121
MOS_MIGRATED_REVID=145310121

tools/cpp/wrapper/bin/call_python.bat.tpl

@@ -14,7 +14,7 @@
 
 :: Invoke the python script under pydir with the same basename
 @echo OFF
-set arg0=%1
+set arg0=%~1
 for %%F in ("%arg0%") do set DRIVER_BIN=%%~dpF
 
 for /F %%i in ("%arg0%") do set TOOLNAME=%%~ni