mk: Add NO_MKFILE_DEPS for turning off rebuild from makefile changes

Author: brson

Makefile.in

@@ -37,6 +37,7 @@
 #                          (may require `CFG_ENABLE_VALGRIND`)
 # * `NO_REBUILD=1` - Don't rebootstrap when testing std
 #                    (and possibly other crates)
+# * `NO_MKFILE_DEPS=1` - Don rebuild for modified .mk files
 # * `SAVE_TEMPS=1` - Use `--save-temps` flag on all `rustc` invocations
 # * `ASM_COMMENTS=1` - Use `-Z asm-comments`
 # * `TIME_PASSES=1` - Use `-Z time-passes`

mk/main.mk

@@ -12,7 +12,11 @@
 # and include all of the .d files in one fell swoop.
 ALL_OBJ_FILES :=
 
+ifneq ($(NO_MAKEFILE_DEPS),)
+MKFILE_DEPS :=
+else
 MKFILE_DEPS := config.stamp $(call rwildcard,$(CFG_SRC_DIR)mk/,*)
+endif
 NON_BUILD_HOST = $(filter-out $(CFG_BUILD),$(CFG_HOST))
 NON_BUILD_TARGET = $(filter-out $(CFG_BUILD),$(CFG_TARGET))