GCC can support using zstd compression for LTO object files. By default
GCC's configure will enable this if libzstd is installed on the machine
building the toolchain. This may be undesirable if the toolchain is to
be used on a different machine. Add an option to control zstd usage and
set the default to the same as the current behaviour (i.e. auto).
Fixes#1579
Signed-off-by: Chris Packham <judge.packham@gmail.com>
b346fa58b1