proc_service.h provides some declarations used when implementing the
API used by libthread_db to find TLS locations.

This file is included in rr because it currently isn't installed by
glibc.  There is a glibc bug open to address this:

    https://sourceware.org/bugzilla/show_bug.cgi?id=20311

However, rather than use the glibc version of this file and attempt to
understand what the LGPL means, we've imported a version from FreeBSD;
but slightly modified.  In particular, we:

* Removed __BEGIN_DECLS and __END_DECLS uses
* Renamed ps_pread and ps_pwrite to match glibc's names
* Added declarations for ps_getpid and ps_get_thread_area
* Reordered ps_err_e so that enumerators have the correct values
