Remove $FreeBSD$: one-line sh pattern

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

tools: minor spelling fixes.

Mostly comments but also some user-visible strings.

MFC after: 2 weeks

Use print as a function for Python 3 [PEP 3105]

Import print_function from the __future__ module
to activate this for Python 2. This works as far back as Python 2.6.0a2:
https://docs.python.org/2/library/__future__.html

[PEP 3105] https://www.python.org/dev/peps/pep-3105/

Use 'in' instead of 'has_key()' for testing dictionary membership.

In PEP 0290, has_key() was deprecated in Python 2.2 and higher:
https://www.python.org/dev/peps/pep-0290/#testing-dictionary-membership
https://docs.python.org/2.2/whatsnew/node4.html

In Python 3, dict.has_key() was removed:
https://docs.python.org/3.0/whatsnew/3.0.html#builtins

Update tools/shlib-compat.

- Update dwarfdump / compiler support.
Use hex instead of decimal for integers.
Add boolean and restrict type definitions.
Add options for specifing dwarfdump and objdump executables.

- Fix reporting missing symbol definitions as matching.

- Compare external variable definitions.

- Exclude special symbols like _init, _end by default.

- Fix test build.

Add shlib-compat under tools.

shlib-compat is ABI compatibility checker for shared libraries with
symbol versioning.