kernel.bbclass: enable a link for external module building

Even though the kernel-dev package provides the required support for
building external kernel modules on the target, some commonly used scripts
and utilities fail as they are not finding the kernel module build support
files at the desired location.

Create the /lib/modules/<kernel-version>/build link on target pointing to
the sources provided by the kernel-dev package, to fix the issue.

Fixes Bug:
[YOCTO #2968]

Signed-off-by: Nitin A Kamble <nitin.a.kamble@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
gcc-runtime: Add linux-gnuspe symlink

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
meta-environment: Deal with machines which change TARGET_OS

Some machines change TARGET_OS, cross-canadian resets this which
is not what we want in this specific case. This fixes spe toolchains
for example.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
cross-canadian: Disable the packagedata stamp-extra-info

Similarly to native/cross disable this since otherwise the packagedata
can be marked as machine specific and if you switch machines
which share an arciteture, you'll get toolchain overlapping files
errors.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>