firmware/build: Use gnu99 coding convention

C99 doesn't require/support anonymous struct/unions in some GCC versions
and those are used a lot.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
libhackrf: Add a pkgconfig .pc file to allow auto-discovery of prefix

Shamelessly copied from librtlsdr.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
libhackrf: Fix early exit of transfer thread in case of syscal interruption

libusb can return LIBUSB_ERROR_INTERRUPTED and it's not really an error,
just a sign some syscall got interrupted by something. Don't abort on
that.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Merge pull request #68 from smunaut/pending

Misc patches I needed to make it work properly