Dear notmuch,

Although notmuch was configuring fine on FreeBSD before 3c13bc, the pkg-config
check introduced for zlib does not work. Indeed, zlib is part of the
base system, and always assumed to be present.

Proposed patch puts platform test before pkg-config checks, and add a
special case for zlib on FreeBSD. uname -U is used to get (numeric) OS version,
and compared to lowest release where at least zlib 1.2.5.2 was available
(that’s FreeBSD 9.1, with zlib 1.2.7).

Best,

--
Xīcò