rtld: Add support for LD_LIBRARY_PATH_FDS env variable

This variable allows loading of shared libraries via directory descriptors
rather than via library paths. if LD_LIBRARY_PATH_FDS=3:4:12, the
di

rtld: Add support for LD_LIBRARY_PATH_FDS env variable

This variable allows loading of shared libraries via directory descriptors
rather than via library paths. if LD_LIBRARY_PATH_FDS=3:4:12, the
directories represented by file descriptors 3, 4, and 12 will be searched
for shared libraries before the normal path-based mechanisms are used.
This allows the execution of unpriviledge binaries from within a Capsicum
sandbox even if they require shared libraries. Note that Capsicum is not
available on DragonFly yet.

While here, adjust whitespace and rearrange a bit to minimize differences
with FreeBSD rtld.

Taken from: FreeBSD svn 267678 (20 June 2014)

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rtld: Make thread-safe by replacing libc printf functions

The dynamic linker is linked with the specially built static pic libc to
get some C runtime services such as printf(). Unfortunately, the
m

rtld: Make thread-safe by replacing libc printf functions

The dynamic linker is linked with the specially built static pic libc to
get some C runtime services such as printf(). Unfortunately, the
multithread-safeness measures in libc do now work in the rtld environment.

The dynlinker now uses FreeBSD's kernel printf() implementation instead of
libc's version. This printf does not require any shared global data and
thus is mt-safe. This commit replaces printf() and related functions with
rtld_ versions, and also removes calls to err(3).

Currently stdio is still pulled from libc within the libmap implementation
that uses fopen(). This is safe, yet not optimal, and is a candidate for
future change.

The makefile was cleaned up to remove the unused bits to building an
executable dynlinker and also require gnu99.

Taken-from: FreeBSD SVN 225152

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