Hello automakers.  The reasons of this patch should be
explained in details in the ChangeLog entry (see below).

OK for the 'yacc-work' branch?

Regards,
   Stefano

-*-*-

With this change, if '-d' is in *YFLAGS, a yacc input file named
foo.y++ will cause a foo.h++ header to be generated, instead of a
foo.h header.  Similarly for foo.ypp, foo.yxx and foo.yy.
This way, the name of the files generated by an automake-created
`ylwrap' invocation should be consistent with those generated by
a `bison -o' call.

Related to automake bug#7648 and PR automake/491.

* lib/am/yacc.am (am__yacc_c2h): New internal variable.
(?GENERIC?%EXT%%DERIVED-EXT%, ?!GENERIC?%OBJ%): Get the name of
the header dynamically at make runtime, so that its extension is
modelled after the extension of the source.
* automake.in (lang_yacc_target_hook): Adjust the calculation of
`$header' accordingly.
* tests/yacc-cxx.test: New test.
* tests/yacc-d-cxx.test: Likewise.
* tests/yacc-weirdnames.test: Likewise.
* tests/yacc-basic.test: Update comments.
* tests/yacc-d-basic.test: Likewise.
* tests/yaccpp.test: Updated and extended.
* tests/Makefile.am (TESTS): Update.