Add RLIM_SAVED_MAX and RLIM_SAVED_CUR symbols.

Define them as RLIM_INFINITY. This is allowed by POSIX in case all
resource limits are representable in an object of type rlim_t. Since
we do not allow negative rlim_t, with some strength this definition is
conforming.

We are not conforming fully still because POSIX requires rlim_t to be
unsigned type. Fixing this without breaking ABI to redefine
RLIM_INFINITY is impossible.

PR: 209729
Submitted by: bltsrc@mail.ru
Exp-run done by: antoine
MFC after: 2 weeks