configure.ac: fails if yacc is not available

configure.ac

@@ -1121,7 +1121,11 @@ fi
 
 # Bison is used to generate the C expression parser.  The generated
 # parser is part of the distribution, though.
-AC_PROG_YACC
+AC_PATH_PROG([YACC], [yacc])
+AC_MSG_CHECKING(yacc $YACC)
+if test "x$YACC" = "x"; then
+    AC_MSG_ERROR([Compiler yacc not available])
+fi
 
 AM_CONDITIONAL([BUILD_GCC_PLUGIN], [test "x$build_gcc_plugin" = "xyes"])
 AM_CONDITIONAL([HAVE_GUILE], [test "x$GUILE" != "x"])