We rely on the include path to find many of these headers. It
especially doesn't make sense to use #include "foo.h" for headers
in the top-level include directory.
If the .so file is missing but the .a file exists, try to dlopen()
the AIX .a file using the .so name as the member. We need to avoid
breaking existing configurations if the type of AIX shared library
changes when sudo is upgraded.
For AIX, if dlopen() fails we try again with RTLD_MEMBER set
and a default member (shr.o or shr_64.o). However, if that
also fails, the user will receive a useless error message
that doesn't correspond to the actual problem. We now retry
the original dlopen() if the fallback to RTLD_MEMBER fails,
which has the effect of restoring the original error message.
It is possible to specify the member name in parens after the path,
e.g. sudoers.a(shr.o) for 32-bit or sudoers.a(shr_64.o) for 64-bit.
If no member is specified in the path and dlopen() fails with ENOEXEC,
try again with an explicit member, either shr.o or shr_64.o.
Previously we needed to include headers required by the various
sudo*h files. Now those files are more self-sufficient and we
should only include headers needed by code in the various .c files.
