add OpenVDB

[Crghilardi]

This PR adds a build_tarballs.jl for the OpenVDB library.

working on x86_64-linux-gnu, not sure if this is going to work on musl due to pthreads things?

[giordano]

Musl platforms are failing with

[00:56:28] ccache /opt/bin/x86_64-linux-musl-libgfortran4-cxx11/x86_64-linux-musl-g++ --sysroot=/opt/x86_64-linux-musl/x86_64-linux-musl/sys-root/  -O3 -DNDEBUG   CMakeFiles/vdb_print.dir/openvdb_print.cc.o  -o vdb_print  -Wl,-rpath,/workspace/srcdir/openvdb-8.2.0/build/openvdb/openvdb:/usr/local/lib:/workspace/destdir/lib: ../libopenvdb.so.8.2.0 /opt/x86_64-linux-musl/x86_64-linux-musl/sys-root/usr/local/lib/libjemalloc.so /opt/x86_64-linux-musl/x86_64-linux-musl/sys-root/usr/local/lib/libtbb.so /opt/x86_64-linux-musl/x86_64-linux-musl/sys-root/usr/local/lib/libblosc.so /opt/x86_64-linux-musl/x86_64-linux-musl/sys-root/usr/local/lib/libz.so /workspace/destdir/lib/libboost_iostreams.so.1.76.0 /workspace/destdir/lib/libboost_system.so.1.76.0 
[00:56:29] /opt/x86_64-linux-musl/x86_64-linux-musl/sys-root/usr/local/lib/libtbb.so: undefined reference to `getcontext'
[00:56:29] /opt/x86_64-linux-musl/x86_64-linux-musl/sys-root/usr/local/lib/libtbb.so: undefined reference to `swapcontext'
[00:56:29] /opt/x86_64-linux-musl/x86_64-linux-musl/sys-root/usr/local/lib/libtbb.so: undefined reference to `makecontext'
[00:56:29] collect2: error: ld returned 1 exit status
[00:56:29] make[2]: *** [openvdb/openvdb/cmd/CMakeFiles/vdb_print.dir/build.make:111: openvdb/openvdb/cmd/vdb_print] Error 1

Quoting from https://wiki.musl-libc.org/open-issues.html#ucontext.h (popped up also in https://github.com/JuliaPackaging/Yggdrasil/pull/1694#issuecomment-698052349)

Legacy functions operating on ucontext_t (getcontext, setcontext, makecontext, swapcontext) are not implemented. They are no longer part of POSIX, but cooperative multi-tasking applications use them. ucontext_t also appears as an argument to sigaction handlers which cannot be used portably.

I don't think there is anything we can do for these platforms (unless someone wants to patch upstream to completely avoid these functions). This means oneTBB is really unusable with Musl.

[giordano]

Oh, wait: https://github.com/oneapi-src/oneTBB/pull/748

[Crghilardi]

Oh cool, I guess this will need to wait for the next release of oneTBB.

One thing I am not clear on is how it's picking Jemalloc vs TBBalloc? According to the top level CMake but I tried compiling without oneTBB and it errored out on me.