binutils/gcc/gdb: Add TARGET_ARCH to PN for all cross recipes

This allows them to co-exist together in the native sysroot, with one
set of cross tools per target architecture.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
gcc-target: Limit compile to host targets, don't build runtimes.

Currently the gcc builds are building copies of the target libraries
that we never use (it isn't installed in do_install). This is a rather
pointless waste of cpu time.

Instead just compile the host targets. Comparing the package output of
this compared to a previous build shows that the unwind.h header is
missing since its provided by gcc. Fix this simply by copying it in.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
gcc-common/gcc-configure-common: Move gnu-configize to its own shared task

This command modifies ${S} and can race against other tasks running do_configure and
having the scripts disappear from under them. To avoid this move to its own
task and work on the shared work directory as a common task.

It needs to be a python task to avoid lots of shell exported variables as
dependencies.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
gcc: Drop ARCH_FLAGS_FOR_TARGET usage

As far as I can tell this variable is now completely unneeded. It would
only ever get used in target builds and these are now correctly done
in the target environment namespace, not any of our cross environments.
As such, CC and other variables contain the correct compilers and other
tune options and these are correctly picked up when building libgcc,
libstdc++ and others.

I tried to figure out where else these would make any sense and couldn't
find anything. Builds appear fine without them so lets drop the complexity
including the patch adding in this flag to gcc.

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