examples: add a demonstration of GLR parsers in C

Based on the test case 668 (cxx-type.at:437) "GLR: Merge conflicting
parses, pure, locations".

* examples/c/glr/Makefile, examples/c/glr/README.md,
* examples/c/glr/c++-types.test, examples/c/glr/c++-types.y,
* examples/c/glr/local.mk: New.

examples/c/glr/Makefile

@@ -0,0 +1,28 @@
+# This Makefile is designed to be simple and readable.  It does not
+# aim at portability.  It requires GNU Make.
+
+BASE = calc
+BISON = bison
+XSLTPROC = xsltproc
+
+all: $(BASE)
+
+%.c %.h %.xml %.gv: %.y
+	$(BISON) $(BISONFLAGS) --defines --xml --graph=$*.gv -o $*.c $<
+
+$(BASE): $(BASE).o
+	$(CC) $(CFLAGS) -o $@ $^
+
+run: $(BASE)
+	@echo "Type arithmetic expressions.  Quit with ctrl-d."
+	./$<
+
+html: $(BASE).html
+%.html: %.xml
+	$(XSLTPROC) $(XSLTPROCFLAGS) -o $@ $$($(BISON) --print-datadir)/xslt/xml2xhtml.xsl $<
+
+CLEANFILES =									\
+  $(BASE) *.o $(BASE).[ch] $(BASE).output $(BASE).xml $(BASE).html $(BASE).gv
+
+clean:
+	rm -f $(CLEANFILES)