libc/glibc: install obsolete RPC for both eglibc and glibc

Currently, the obsolete RPC headers are only installed for eglibc,
but glibc has the same /deficiency/, so install the obsolete RPC
for both.

Signed-off-by: Jérôme BARDON <bardon.pro@gmail.com>
Signed-off-by: David Holsgrove <david.holsgrove@xilinx.com>