Don't run findleaves.sh if we're doing ONE_SHOT_MAKEFILE.

This cuts the minimum mmm time from 17 seconds to 5 seconds on my mac pro.
diff --git a/core/main.mk b/core/main.mk
index 59d216f..c3f1e2f 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -327,8 +327,6 @@
 # Bring in all modules that need to be built.
 ifneq ($(dont_bother),true)
 
-subdir_makefiles :=
-
 ifeq ($(HOST_OS),windows)
 SDK_ONLY := true
 endif
@@ -426,15 +424,6 @@
 
 endif	# !SDK_ONLY
 
-# Can't use first-makefiles-under here because
-# --mindepth=2 makes the prunes not work.
-subdir_makefiles += \
-	$(shell build/tools/findleaves.sh --prune="./out" $(subdirs) Android.mk)
-
-#
-# Include all of the makefiles in the system
-#
-
 ifneq ($(ONE_SHOT_MAKEFILE),)
 # We've probably been invoked by the "mm" shell function
 # with a subdirectory's makefile.
@@ -450,9 +439,21 @@
 # when using ONE_SHOT_MAKEFILE.
 NOTICE-HOST-%: ;
 NOTICE-TARGET-%: ;
-else
+
+else # ONE_SHOT_MAKEFILE
+
+#
+# Include all of the makefiles in the system
+#
+
+# Can't use first-makefiles-under here because
+# --mindepth=2 makes the prunes not work.
+subdir_makefiles := \
+	$(shell build/tools/findleaves.sh --prune="./out" $(subdirs) Android.mk)
+
 include $(subdir_makefiles)
-endif
+endif # ONE_SHOT_MAKEFILE
+
 # -------------------------------------------------------------------
 # All module makefiles have been included at this point.
 # -------------------------------------------------------------------