refactor: limit quotes to terms with spaces

during testing it was extremely helpful having the error identify
which vswhere command had been executed, and even more helpful
being able to paste it.

since most visual studio paths have spaces in them, that's not
possible unless those terms have quotes around them, e.g.

"C:\Program Files (x86)\Microsoft\Visual Studio\...\vswhere.exe" -products ...

cpython-windows/build.py

@@ -260,8 +260,10 @@ def find_vs_path(path, msvc_version):
     ]
     p = subprocess.check_output(cmdline)
     if not p:
-        cmd = " ".join('"%s"' % i for i in cmdline)
-        print("could not find visual studio (using '%s')" % cmd)
+        # add quotes around any of the terms with spaces in them, so that
+        # the user can copy-and-paste the command.
+        cmdline = ['"%s"' % term if " " in term else term for term in cmdline]
+        print("could not find visual studio (using '%s')" % cmdline)
         sys.exit(1)
 
     # Strictly speaking the output may not be UTF-8.