examples: add a complete example with all the bells and whistles

* examples/c/bistromathic/Makefile,
* examples/c/bistromathic/README.md,
* examples/c/bistromathic/bistromathic.test,
* examples/c/bistromathic/local.mk,
* examples/c/bistromathic/parse.y,
* examples/c/bistromathic/scan.l:
New.

* Makefile.am (AM_YFLAGS_WITH_LINES): Add -Wdangling-alias.
* examples/test: Make failure errors easier to read.

examples/c/bistromathic/local.mk

@@ -0,0 +1,36 @@
+## Copyright (C) 2020 Free Software Foundation, Inc.
+##
+## This program is free software: you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+bistromathicdir = $(docdir)/%D%
+
+## --------------- ##
+## Bistromathics.  ##
+## --------------- ##
+
+if FLEX_WORKS
+  check_PROGRAMS += %D%/bistromathic
+  TESTS += %D%/bistromathic.test
+  EXTRA_DIST += %D%/bistromathic.test
+  nodist_%C%_bistromathic_SOURCES = %D%/parse.y %D%/parse.h %D%/scan.l
+  %D%/calc.c: $(dependencies)
+
+  # Don't use gnulib's system headers.
+  %C%_bistromathic_CPPFLAGS = -I$(top_srcdir)/%D% -I$(top_builddir)/%D%
+  %C%_bistromathic_LDADD = -lm
+endif FLEX_WORKS
+
+dist_bistromathic_DATA = %D%/parse.y %D%/scan.l %D%/Makefile %D%/README.md
+CLEANFILES += %D%/parse.[ch] %D%/scan.c %D%/parse.output
+CLEANDIRS += %D%/*.dSYM