Enable threadsafe

--enable-unsupported is necesssary for HDF5 to build with both
threadsafety and high level library enabled.

--with-pthreads form HDF5 docs and conda-forge

Thread safety flags copied from conda-forge hdf5-feedstock:
conda-forge/hdf5-feedstock@36304eabd09a68d60a726fd6de4913d38c040917

library_builders.sh

@@ -227,7 +227,8 @@ function build_hdf5 {
     local short=$(echo $HDF5_VERSION | awk -F "." '{printf "%d.%d", $1, $2}')
     fetch_unpack $hdf5_url/hdf5-$short/hdf5-$HDF5_VERSION/src/hdf5-$HDF5_VERSION.tar.gz
     (cd hdf5-$HDF5_VERSION \
-        && ./configure --with-szlib=$BUILD_PREFIX --prefix=$BUILD_PREFIX --enable-threadsafe \
+        && ./configure --with-szlib=$BUILD_PREFIX --prefix=$BUILD_PREFIX \
+        --enable-threadsafe --enable-unsupported --with-pthread=yes \
         && make -j4 \
         && make install)
     touch hdf5-stamp