guile: Add new package

Guile is an interpreter and compiler for the Scheme programming
language, a clean and elegant dialect of Lisp.

The patch guile-01-fix_arm_endianness.patch is based on guile's
git commit ^ffd3e55cfd

[Thomas:
 - rewrap comments and help text.
 - add missing host-gettext dependency, since gettext.m4 is needed for
   the package to autoreconf.
 - add missing host-pkgconf dependency.
 - add dependency on wchar, inherited from libunistring.]

Signed-off-by: Pedro Aguilar <paguilar@paguilar.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>