apply stdlib transformations

recipe/conda_build_config.yaml

@@ -1,3 +1,3 @@
 # Bump MacOs target to 10.13 for Boost.Cobalt / C++20 support
-MACOSX_DEPLOYMENT_TARGET:
+c_stdlib_version:   # [osx and x86_64]
   - '10.13' # [osx and x86_64]

recipe/meta.yaml

@@ -36,6 +36,7 @@ build:
 requirements:
   build:
     - {{ compiler('cxx') }}
+    - {{ stdlib('c') }}
     - cross-python_{{ target_platform }}     # [build_platform != target_platform]
     - python {{ PY_DUMMY_VER }}.* *_cpython  # [build_platform != target_platform]
     - numpy {{ NP_DUMMY_VER }}.*             # [build_platform != target_platform]
@@ -98,15 +99,14 @@ outputs:
       build:
         # for strong run-exports
         - {{ compiler('cxx') }}
+        - {{ stdlib('c') }}
       host:
         - icu               # [unix]
         - libiconv          # [win]
         - bzip2
         - xz
         - zlib
         - zstd
-      run:
-        - __osx >={{ MACOSX_DEPLOYMENT_TARGET|default("10.9") }}  # [osx and x86_64]
       run_constrained:
         # Anaconda's output is also called libboost; therefore we automatically
         # avoid issues of co-installability, because a package with the same name
@@ -233,6 +233,7 @@ outputs:
         - cross-python_{{ target_platform }}     # [build_platform != target_platform]
         - numpy                                  # [build_platform != target_platform]
         - {{ compiler('cxx') }}
+        - {{ stdlib('c') }}
       host:
         # ensure python_impl gets picked up by smithy (by using it as a selector) and therefore
         # populated in the .ci_config/*.yaml files, for use in {build,install}-py.{sh,bat}.