tests/run-tests: Add cmd line option "--heapsize".

This allows you to specify the heapsize that unix will use when running
the test suite, eg: ./run-tests --heapsize 16k

tests/run-tests

@@ -140,7 +140,11 @@ def run_micropython(pyb, args, test_file):
         else:
             # a standard test
             try:
-                output_mupy = subprocess.check_output([MICROPYTHON, '-X', 'emit=' + args.emit, test_file])
+                cmdlist = [MICROPYTHON, '-X', 'emit=' + args.emit]
+                if args.heapsize is not None:
+                    cmdlist.extend(['-X', 'heapsize=' + args.heapsize])
+                cmdlist.append(test_file)
+                output_mupy = subprocess.check_output(cmdlist)
             except subprocess.CalledProcessError:
                 output_mupy = b'CRASH'
     else:
@@ -344,6 +348,7 @@ def main():
     cmd_parser.add_argument('-d', '--test-dirs', nargs='*', help='input test directories (if no files given)')
     cmd_parser.add_argument('--write-exp', action='store_true', help='save .exp files to run tests w/o CPython')
     cmd_parser.add_argument('--emit', default='bytecode', help='MicroPython emitter to use (bytecode or native)')
+    cmd_parser.add_argument('--heapsize', help='heapsize to use (use default if not specified)')
     cmd_parser.add_argument('files', nargs='*', help='input test files')
     args = cmd_parser.parse_args()