The current .pc generated by make build system for zstd is wrong and
always assume a single-threaded library is used.
This wasn't the case for the meson build system that used his own logic
to generate the pkg-config file.
Add a patch to fix this by introducing install-mt-pc make target to
generate the correct pkg-config gile.
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
