Add DEPEND_MAKEFILE to disable rebuild on Makefile edit

Makefile

@@ -3,10 +3,6 @@
 #
 # GNU Make required
 #
-
-# Rebuild every target if Makefile changes
-.EXTRA_PREREQS:= $(abspath $(lastword $(MAKEFILE_LIST)))
-
 COMPILE_PLATFORM=$(shell uname | sed -e 's/_.*//' | tr '[:upper:]' '[:lower:]' | sed -e 's/\//_/g')
 COMPILE_ARCH=$(shell uname -m | sed -e 's/i.86/x86/' | sed -e 's/^arm.*/arm/')
 
@@ -3210,6 +3206,11 @@ dist:
 # DEPENDENCIES
 #############################################################################
 
+# Rebuild every target if Makefile or Makefile.local changes
+ifneq ($(DEPEND_MAKEFILE),0)
+.EXTRA_PREREQS:= $(MAKEFILE_LIST)
+endif
+
 ifneq ($(B),)
   OBJ_D_FILES=$(filter %.d,$(OBJ:%.o=%.d))
   TOOLSOBJ_D_FILES=$(filter %.d,$(TOOLSOBJ:%.o=%.d))

README.md

@@ -133,6 +133,8 @@ The following variables may be set, either on the command line or in
 Makefile.local:
 
 ```
+  DEPEND_MAKEFILE      - set to 0 to disable rebuilding all targets when
+                         the Makefile or Makefile.local is changed
   CFLAGS               - use this for custom CFLAGS
   V                    - set to show cc command line when building
   DEFAULT_BASEDIR      - extra path to search for baseq3 and such