Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

check-links.sh: treat PIE executable as elf files

Allow specifying an alternative LD_LIBRARY_PATH for the ldd(1) lookup.

This is needed to be able to run check-links.sh against a "sysrooted"
binary while ensuring that the ldd(1) call done on the host uses the
host libc. It is not possible to set LD_LIBRARY_PATH before calling
check-links.sh as then the "sysrooted" libc would be incorrectly used.

A LD_PRELOAD=libc.so is used to ldd(1) as it needs to use the host libc
to run. ldd(1) is a simple wrapper around execve(2) and dlopen(2) with
env LD_TRACE_LOADED_OBJECTS set. Due to the dlopen(2) restriction on
shared library tracing ldd(1) is still required for this lookup.

Sponsored by: EMC / Isilon Storage Division

Add some documentation.

Sponsored by: EMC / Isilon Storage Division

Validate that the file exists rather than obscure 'Not an elf file' error.

Sponsored by: EMC / Isilon Storage Division

Add a -v to tell where each symbol is resolved from.

Sponsored by: EMC / Isilon Storage Division

Fix a comment

Tweak BSS symbol handling from r281811 to not consider them unresolved

Support libraries linked by path.

Sponsored by: EMC / Isilon Storage Division

- For executables search for matching (B) global uninitialized BSS symbols from
linked libraries. Only do this for BSS symbols that have a size which avoids
__bss_start. Without this some libraries would be considered unneeded even
though they were providing a B symbol.
- Add in the symbols from crt1.o to cover a handful of common unresolved symbols.
- Consider (C) common data symbols as provided by libraries/crt1.
- Move libkey() function to more appropriate place.

Sponsored by: EMC / Isilon Storage Division

Revert r281805 for now as it breaks due to spaces in output

Pass full path to ldd(1) so it works on files in cwd.

Support demangling C++ symbols with -D flag.

Sponsored by: EMC / Isilon Storage Division

- Speedup significantly by not using subshells for data already fetched.
Ran against /usr/local/sbin/pkg:
Before: 25.12 real 12.41 user 33.14 sys
After: 0.53 real 0.49 user 0.13 sys
- Exit with 1 if any missing or unresolved symbol is detected.
- Add option '-U' to skip looking up unresolved symbols.
- Don't consider provided weak objects as unresolved (nm V).

Sponsored by: EMC / Isilon Storage Division

Fix indentation to use tabs

- Fix support with new elftoolchain readelf(1)
- Fix not finding global symbols by checking for D and R.
- Follow symlinks
- Show which matching symbol was used to consider the library needed.

Discussed with: bapt

Add a quick and dirty script to check validity of links in elf files