nfs-utils: Include legacy or TI-RPC headers, not both

nfs-utils: Include legacy or TI-RPC headers, not both

Data type incompatibilities between the legacy RPC headers and the
TI-RPC headers mean we can't use libtirpc with code that was compiled
against the legacy RPC headers.  The definition of rpcprog_t for
example is "unsigned long" in the legacy library, but it's "uint32_t"
for TI-RPC.  On 32-bit systems, these types happen to have the same
width, but on 64-bit systems they don't, making more complex data
structures that use these types in fields ABI incompatible.

Adopt a new strategy to deal with this issue.  When --enable-tirpc is
set, append "-I/usr/include/tirpc" to the compilation steps.  This
should cause the compiler to grab the tirpc/ headers instead of the
legacy headers.  Now, for TI-RPC builds, the TI-RPC legacy functions
and the TI-RPC headers will be used.  On legacy systems, the legacy
headers and legacy glibc RPC implementation will be used.

A new ./configure option is introduced to allow system integrators to
use TI-RPC headers in some other location than /usr/include/tirpc.
/usr/include/tirpc remains the default setting for this new option.

The gssd implementation presents a few challenges, but it turns out
the gssglue library is similar to the auth_gss pieces of TI-RPC.  To
avoid similar header incompatibility issues, gssd now uses libtirpc
instead of libgssglue if --enable-tirpc is specified.  There may be
other issues to tackle with gssd, but for now, we just make sure it
builds with --enable-tirpc.

Note also: svc_getcaller() is a macro in both cases that points to
a sockaddr field in the svc_req structure.  The legacy version points
to a sockaddr_in type field, but the TI-RPC version points to a
sockaddr_in6 type field.

rpc.mountd unconditionally casts the result of svc_getcaller() to a
sockaddr_in *.  This should be OK for TI-RPC as well, since rpc.mountd
still uses legacy RPC calls (provided by glibc, or emulated by TI-RPC)
to set up its listeners, and therefore rpc.mountd callers will always
be from AF_INET addresses for now.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>