update Dockerfile and fix root build error (see MLton#601)

Dockerfile

@@ -5,14 +5,16 @@ RUN apt-get update -qq \
  && apt-get install -qq git build-essential libgmp-dev mlton mlton-tools vim \
  && git clone https://github.com/mlton/mlton.git /root/mlton \
  && cd /root/mlton \
- && git checkout on-20210117-release \
+ && git checkout on-20241230-release \
  && make
 
-ENV PATH /root/mlton/build/bin:$PATH
+ENV PATH=/root/mlton/build/bin:$PATH
 
 # Copy the current directory (MPL source root) to a location within the container & move there
 COPY . /root/mpl
 WORKDIR /root/mpl
 
 # Build from source, install, and make examples
 RUN make && make install && cd examples && make
+
+ENV PATH=/root/mpl/build/bin:$PATH

mlton/Makefile

@@ -109,12 +109,12 @@ front-end/%.lex.sml: front-end/%.lex
 	$(SED) -e 's/in Vector.fromList(List.map g/in Vector.fromList(Pervasive.List.map g/' $<.sml.in > $<.sml
 	$(RM) $<.sml.in
 	$(CP) $<.sml $<.sml.boot
-	$(CHMOD) -w $<.*
+	$(CHMOD) a-w $<.*
 else
 front-end/%.lex.sml: front-end/%.lex.sml.boot
 	$(RM) $@
 	$(CP) $< $@
-	$(CHMOD) -w $@
+	$(CHMOD) a-w $@
 endif
 
 ifeq (true,$(call HAVE_CMD,$(RUN_MLYACC)))
@@ -131,16 +131,16 @@ front-end/%.grm.sig front-end/%.grm.sml: front-end/%.grm
 	$(SED) -e 's/in Array.fromList(List.map actionRowLookUp actionRowNumbers)/in Array.fromList(Pervasive.List.map actionRowLookUp actionRowNumbers)/' $<.sml.in > $<.sml
 	$(RM) $<.sml.in
 	$(CP) $<.sml $<.sml.boot
-	$(CHMOD) -w $<.*
+	$(CHMOD) a-w $<.*
 else
 front-end/%.grm.sig: front-end/%.grm.sig.boot
 	$(RM) $@
 	$(CP) $< $@
-	$(CHMOD) -w $@
+	$(CHMOD) a-w $@
 front-end/%.grm.sml: front-end/%.grm.sml.boot
 	$(RM) $@
 	$(CP) $< $@
-	$(CHMOD) -w $@
+	$(CHMOD) a-w $@
 endif
 
 mlton-stubs.mlb: $(shell $(MLBDEPS) ../lib/stubs/mlton-stubs/sources.mlb | $(GREP) 'mlb$$' | $(GREP) -v '$$(SML_LIB)') $(shell $(MLBDEPS) mlton.mlb | $(GREP) 'mlb$$' | $(GREP) -v '$$(SML_LIB)')