[U-Boot] standalone-examples: support custom GCC lib

[Jack Mitchell]

Fighting with compiling u-boot today and dealing with problems related
to using a custom built openembedded toolchain, I found the need to
specify a custom location for the GCC lib.

This is well supported when building u-boot, but my compile was failing
in the standalone examples, as there was no support for a custom GCC lib
in the standalone examples Makefile.

I am no toolchain or u-boot expert, and as such to avoid the firey pits
of flamewar hell, this is an RFC ;)

-- 

  Jack Mitchell (jack at embed.me.uk)
  Embedded Systems Engineer
  http://www.embed.me.uk

--