(*.tab.c): Change dependency on Makefile to depend on
Makefile.in, otherwise it always rebuilds after configuring.
Force output *.tab.c file into current directory even in "make"
versions that rewrite dependent file names used in command lines.
* TODO: Remove some things we did.
* am29k-opcode.h, convx-opcode: Remove; now in ../include/opcode.
* os68k-xdep.c: Remove; useless file (os68k is a target only).
* convex-pinsn.c: Use ../include/opcode/convex.h. Add CONST.
* symtab.h: Eliminate unnamed unions and structs.
* All GDB files that #include defs.h: Removed stdio.h.
(defs.h): #include stdio.h.
This has been tested by building GDBs for all targets hosted on Sun4.
None of the build problems were related to stdio.h inclusion. (n.b.
many configurations don't build for other reasons.)