test-suite: Added new test suite feature (experimental)

This patch adds support for installing the gcc test suite. A helper
Makefile is provided for building and running the gcc tests.

The default configuration runs all gcc tests and requires automatic
ssh/scp login access to a networked target board. See README for
more details.

Note: Current feature is tested with the powerpc-unknown-linux-gnu
sample but it should work with others as well.

Signed-off-by: Martin Lund <mgl@doredevelopment.dk>

scripts/wrapper.c: Under MacOS set DYLD_LIBRARY_PATH

Depending on (predefined) macro __APPLE__, use DYLD_LIBRARY_PATH
instead of LD_LIBRARY_PATH.

docs/overview.txt: Provide short mercurial HOWTO

The usage of hg mq is imho not very well documented.
Give a short intro for the most important use cases
for contributions to ct-ng.

yann.morin.1998@anciens.enib.fr:
Slightly rewrote the explanations for the introductory message.

ct-ng: Add ability to configure and use some GNU tools

Make the paths to libtool, objcopy, objdump, readelf, patch configurable.

scripts/build/internals.sh: Always use binary wrapper under BSD/MacOS

The shell wrapper script uses a nonportable call to readlink.
Thus, always use the binary wrapper under BSD/MacOS.

yann.morin.1998@anciens.enib.fr:
Use 'case' instead of 'if'.

scripts/wrapper.in: Add a comment about readlink not being portable.

Documented that the call to readlink will not work on BSD systems.

configure: make call to readlink portable to non-GNU (BSD) systems

The argument '-e' for readlink is a GNU extension.
In setting the variable 'where' the argument '-e' is not necessary, thus eliminated.