Force the %T directory to exist when it is used.

Author: Dave Abrahams

test/lit.cfg

@@ -154,8 +154,10 @@ class SwiftTest(lit.formats.ShTest, object):
         except ValueError: pass
         else:
             test.config.substitutions.pop(percentT_index)
-        test.config.substitutions.append(('%T', tmp_base))
-        
+
+            test.config.substitutions.append(
+                ('%T', '$(mkdir -p %r && echo %r)' % (tmp_base, tmp_base)))
+
         if self.coverage_mode:
             # FIXME: The compiler crashers run so fast they fill up the
             # merger's queue (and therefore the build bot's disk)