Dump temacs in an empty environment to prevent -dev paths from ending
up in the dumped image.

diff --git a/src/Makefile.in b/src/Makefile.in
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -535,7 +535,7 @@ ifeq ($(CANNOT_DUMP),yes)
 	ln -f temacs$(EXEEXT) $@
 else
 	unset EMACS_HEAP_EXEC; \
-	LC_ALL=C $(RUN_TEMACS) -batch $(BUILD_DETAILS) -l loadup dump
+	env -i LC_ALL=C $(RUN_TEMACS) -batch $(BUILD_DETAILS) -l loadup dump
   ifneq ($(PAXCTL_dumped),)
 	$(PAXCTL_dumped) $@
   endif