Fix latent yacc-related bug in gdb/Makefile.in init.c rule

gdb's Makefile.in does not currently scan .y files to add global
initializers from these files to init.c.  However, at least ada-exp.y
tries to use this feature.

This patch fixes the problem.

2016-05-17  Tom Tromey  <tom@tromey.com>

	* Makefile.in (init.c): Search .y files for initialization
	functions.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2016-05-17  Tom Tromey  <tom@tromey.com>
+
+	* Makefile.in (init.c): Search .y files for initialization
+	functions.
+
 2016-05-12  Doug Evans  <dje@google.com>
 
 	PR symtab/19999

gdb/Makefile.in

@@ -1360,6 +1360,7 @@ init.c: $(INIT_FILES)
 	    -e '/version.[co]$$/d' \
 	    -e '/^[a-z0-9A-Z_]*_[SU].[co]$$/d' \
 	    -e '/[a-z0-9A-Z_]*-exp.tab.[co]$$/d' \
+	    -e 's/-exp\.o$$/-exp.y/' \
 	    -e 's/\.[co]$$/.c/' \
 	    -e 's,signals\.c,common/signals\.c,' \
 	    -e 's|^\([^  /][^     ]*\)|$(srcdir)/\1|g' | \