icecc: don't create unnecessary 'ice' dirs in sysroots when disabled

* parsing ICE_PATH="${@icc_path(bb, d)}" causes "ice" directories
  to be created in every sysroot, that could be a bit confusing for
  people who inherit icecc.bbclass, but disabled it
* shorten ICECC_VERSION="${@icc_version(bb, d)}" path a bit
  by returning sooner when disabled
* remove ICECC_PATH and ICECC_ENV_EXEC from signatures, we assume that
  using icecc doesn't influence the output, so it shouldn't matter when
  user supplies own version of icecc or env script

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
gcc-cross: don't create symlinks for tools which don't exist

* g77 and gfortran aren't created by default, so it was creating dangling
  symlinks, which probably doesn't hurt

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
test-dependencies.sh: Redirect stderr

* newer bitbake is printing some messages to stderr, we want to log
  them as well

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Revert "gcc-cross: don't create symlinks for tools which don't exist"

This reverts commit 25682eb37b1871a0f5957fa2ef299db8ccf85316.