The default for m4 is disable gnu options, except for gas.

Makefile

@@ -31,8 +31,10 @@
 # .mig : Currently in use for the wordset, which is a .mi file (WRONG!)
 # It could be, but it has been stolen.
 
-# Would love to use -G but we need the patsubst macro.
-M4=m4 ciforth.m4
+# Normal use of m4
+M4=m4 -G ciforth.m4
+# Only needed for gas where we need the patsubst macro.
+M4_GNU=m4 ciforth.m4
 
 # ALL FILES STARTING IN ``ci86'' (OUTHER ``ci86.gnr'') ARE GENERATED
 
@@ -244,7 +246,7 @@ ci86.%.msm : VERSION %.cfg masm.m4 ci86.gnr
 
 # Using FASM, generating a windows executable on linux.
 ci86.%.fas : VERSION %.cfg fasm.m4 ci86.gnr
-	cat $+ | m4 >$(TEMPFILE)
+	cat $+ | $(M4) - >$(TEMPFILE)
 	sed $(TEMPFILE) -e '/Split here for doc/,$$d' \
 	>$@
 	sed $(TEMPFILE) -e '1,/Split here for doc/d' | \
@@ -255,7 +257,7 @@ ci86.%.fas : VERSION %.cfg fasm.m4 ci86.gnr
 # Now that gas has the .Intel_syntax option, its source can be
 # generated by m4 alone. In particular the order of operands.
 ci86.%.s : VERSION %.cfg gas.m4 ci86.gnr ; \
-	cat $+ | $(M4) - >$(TEMPFILE)
+	cat $+ | $(M4_GNU) - >$(TEMPFILE)
 	sed $(TEMPFILE) -e '/Split here for doc/,$$d' >$@
 	sed $(TEMPFILE) -e '1,/Split here for doc/d' | \
 	sed -e '/Split here for test/,$$d' >$(@:%.s=%.rawdoc)