Using find_package(Threads REQUIRED) instead of linking pthread directly (#1324)

* Linking to Threads::Threads instead of pthread directly 
* moved rt linking to slsSupportObject and only enable for linux

conda-recipes/main-library/build.sh

@@ -19,6 +19,7 @@ cmake .. -G Ninja \
       -DSLS_USE_PYTHON=OFF \
       -DCMAKE_BUILD_TYPE=Release \
       -DSLS_USE_HDF5=OFF \
+      -DSLS_USE_SYSTEM_ZMQ=ON \
      
 NCORES=$(getconf _NPROCESSORS_ONLN)
 echo "Building using: ${NCORES} cores"

conda-recipes/main-library/meta.yaml

@@ -29,6 +29,7 @@ requirements:
     - libtiff
     - zlib
     - expat
+    - zeromq
   
   run:
     - libstdcxx-ng