Log message:
Update graphics/ptex to version 2.4.2

Pkgsrc changes:
Use CMake to check for alloca.h .
Include zlib and pthread in
buildlink3.mk since the are
interface linked in the exported
cmake targets.

Changes:
Export cmake targets to cmake users.
Use newer spinlock API:s on MacOSX.
Use soname versioning.

Log message:
*: Instead of using BUILDLINK_TRANSFORM to force a "gnu" language
variant when a package is using GNU extensions without setting
-std=gnuXX, use FORCE_(C|CXX)_STD.

Log message:
graphics: Replace RMD160 checksums with BLAKE2s checksums

All checksums have been double-checked against existing RMD160 and
SHA512 hashes

Log message:
graphics: Remove SHA1 hashes for distfiles

Log message:
Add missing header.

Log message:
needs zlib

Log message:
Import ptex-2.1.28 as graphics/ptex.

Ptex is a texture mapping system developed by Walt Disney Animation Studios for
production-quality rendering:

 - No UV assignment is required! Ptex applies a separate texture to each face
   of a subdivision or polygon mesh.

 - The Ptex file format can efficiently store hundreds of thousands of texture
   images in a single file.

 - The Ptex API provides cached file I/O and high-quality filtering, everything
   that is needed to easily add Ptex support to a production-quality renderer
   or texture authoring application.