fix: allow CMake to detect if limited API is targeted (#333)

Might be nice if we could indicate the target value too. But that will
still be "truthful", so could be changed later.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: henryiii

src/scikit_build_core/builder/builder.py

@@ -115,7 +115,7 @@ def configure(
         )
         cmake_defines.update(local_def)
 
-        cache_config: dict[str, str | Path] = {
+        cache_config: dict[str, str | Path | bool] = {
             "SKBUILD": "2",
             "SKBUILD_CORE_VERSION": __version__,
         }
@@ -166,6 +166,9 @@ def configure(
             assert isinstance(ext_suffix, str)
             cache_config["SKBUILD_SOABI"] = ext_suffix.rsplit(".", 1)[0].lstrip(".")
 
+        # Allow CMakeLists to detect this is supposed to be a limited ABI build
+        cache_config["SKBUILD_LIMITED_ABI"] = limited_abi
+
         if cache_entries:
             cache_config.update(cache_entries)