Add osx compilers to conda-forge build config

Author: vlad-perevezentsev

conda-recipe-cf/conda_build_config.yaml

@@ -8,6 +8,12 @@ c_stdlib:                     # [linux]
     - sysroot                 # [linux]
 c_stdlib_version:             # [linux]
     - '2.28'                  # [linux]
+c_compiler:                   # [osx]
+    - clang                   # [osx]
+cxx_compiler:                 # [osx]
+    - clangxx                 # [osx]
+c_stdlib:                     # [osx]
+    - macosx_deployment_target  # [osx]
 c_stdlib:                     # [win]
     - vs                      # [win]
 cxx_compiler:                 # [win]