Specify the Python executable on the command line in gm.py

Launching Python scripts can fail on Windows if the Python executable
isn't given as the first argument to the shell. This change adds the
path of the current Python executable, as per the behavior of v8gen.py

Change-Id: Iedaf57bcafc4c6aa6ebb89e945ee967cf393da04
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1497522Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60023}

tools/dev/gm.py

@@ -294,8 +294,9 @@ class Config(object):
       tests = ""
     else:
       tests = " ".join(self.tests)
-    return _Call(os.path.join("tools", "run-tests.py") + " --outdir=%s %s" %
-                   (GetPath(self.arch, self.mode), tests))
+    return _Call('"%s" ' % sys.executable +
+                 os.path.join("tools", "run-tests.py") +
+                 " --outdir=%s %s" % (GetPath(self.arch, self.mode), tests))
 
 def GetTestBinary(argstring):
   for suite in TESTSUITES_TARGETS: