restructured some go wrapper files

Makefile.am

@@ -11,11 +11,54 @@ else
 SUBDIRS += lib mod bin t
 endif
 
-if ENABLE_HCLGO
-SUBDIRS += go
-endif
-
 DIST_SUBDIRS = $(SUBDIRS)
 
 distclean-local:
 	@rm -rf $(top_srcdir)/autom4te.cache
+
+
+clean-local:
+	rm -rf $(builddir)/go.mod $(builddir)/go.sum
+
+if ENABLE_HCLGO
+
+## the attempt to compose a proper procedure using a regular compiler failed.
+## e.g ./configure GOC=opt/go/pkg/tool/linux_amd64/
+## while go.m4 is included in autoconf 2.71, the support for the go language
+## is very limited and the go language itself is pursuing the module based builder.
+##
+## the following is to trick autoconf/automake as if it's building go files with
+## a real compiler whereas the actual building is done thru `go build`
+
+bin_PROGRAMS = hclgo
+hclgo_SOURCES = \
+	go/hcl.go \
+	go/cb.go \
+	go/inst.go \
+	main.go \
+	go.mod
+hclgo_DEPENDENCIES = hclgo.bin
+
+## let the linker to move hclgo.bin to the actual target
+hclgo_LINK = mv -f hclgo.bin hclgo$(EXEEXT) || echo "FAILED TO LINK"
+
+hclgo.bin:
+	cp -pf $(srcdir)/go.mod $(builddir)/go.mod >/dev/null 2>&1 || true
+	chmod u+w $(builddir)/go.mod ## with `make distcheck`, the echo's redirection to the file fails without this permission change
+	sed -ri "/^[[:space:]]*replace[[:space:]]+cfg[[:space:]]*=>/d" $(builddir)/go.mod
+	echo -e "\nreplace cfg => $(abs_builddir)/go/cfg" >> $(builddir)/go.mod
+	[ -f $(srcdir)/go.sum ] && cp -pf $(srcdir)/go.sum $(builddir)/go.sum >/dev/null 2>&1 || true
+	go build -C $(srcdir) -x -o $(abs_builddir)/hclgo.bin -modfile $(abs_builddir)/go.mod
+	go clean -C $(srcdir) -x -modfile $(abs_builddir)/go.mod
+	rm -rf $(builddir)/go.mod $(builddir)/go.sum
+
+## the go to o recipe is fake to deceive make
+.go.o:
+	echo $< > $@
+
+.mod.o:
+	echo $< > $@
+
+endif
+
+