liquid-dsp: new package

[Thomas:
  - add patch to fix autoreconf issue, and use LIQUID_DSP_AUTORECONF =
    YES instead of an horrible hack calling aclocal/autoconf manually.
  - use the github macro instead of hand-coding <pkg>_SITE and
    <pkg>_SITE_METHOD. This allows to remove <pkg>_SITE_METHOD
    entirely.
  - use a full hash as the <pkg>_VERSION
  - remove trailing whitespace everywhere.
  - use one single assignment of LIQUID_DSP_CONF_OPTS
  - fix the comment about the eglibc/musl dependency (it was only
    mentioning eglibc, and the condition was inverted)
  - add the musl/glibc dependency on the package option itself
  - make the package depend on dynamic library support, since the
    makefile unconditionally builds a shared library.
  - add hash file.]

Signed-off-by: Guillaume William Bres <guillaume.bressaix@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>