scons: Ensure config file values are strings.

Apparently, sometimes a SCons Value node created with an integer value
0 will have a string representation which is the empty string, which
is obviously problematic. To work around this bug, convert the value
to a string explicitly before creating the Value node, so that we get
a sensible translation instead.

Change-Id: I4a09b2fb366aaf2d4d1c7e6f8cc84224b2d010c4
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/59472
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Yu-hsin Wang <yuhsingw@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>

site_scons/gem5_scons/builders/config_file.py

@@ -70,7 +70,7 @@ def ConfigFile(env):
         val = env['CONF'][variable]
         if isinstance(val, bool):
             # Force value to 0/1
-            val = int(val)
+            val = str(int(val))
         elif isinstance(val, str):
             val = '"' + val + '"'