* Makefile.in: Add jit-reader.h as a header. Have it installed in
$(includedir)/gdb.
* configure.ac: Generate a correct value for TARGET_PTR for
jit-reader.h. Tell configure to generate jit-reader.h from
jit-reader.in.
* configure: Re-generated by autoconf.
* jit-reader.in: New file.
* jit.c: Include jit-reader.h.