[pkg] glibc: try to deal with the multilib compilers.

The Linaro gcc 4.8 compiler is throwing us a curve ball by offering a
multilib setup with both hard and soft floating point variants. It looks
like their new layout is some kind of default.

  http://lists.linaro.org/pipermail/cross-distro/2012-April/000261.html

In any case, we can improve our search by using '-print-sysroot' when gcc
offers it. It appears that newer versions all do have this flag. We fall
back to the older search method if necessary.

In addition, let us use 'realpath' to beautify the output a bit.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
[pkg] busybox: use the stable 1.20 version.

The earlier 1.19 versions do not compile when using more recent gcc
versions.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
beaglebone: use an even more recent compiler.

There seems to be an issue booting Linux 3.14 using gcc 4.6.1, so lets
jump ahead and use the Linaro 4.8 compiler.

Note that we explicitly place /lib and /usr/lib into the linker path,
because the Linaro compiler does not include these.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
beaglebone: update and expand the readme file.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>