Add CMake install for applicable libraries

Originally developed under https://github.com/pybind/pybind11_abseil/pull/8

PiperOrigin-RevId: 557837688

README.md

@@ -75,6 +75,10 @@ FetchContent_Declare {
 FetchContent_MakeAvailable(pybind11 abseil-cpp pybind11_abseil)
 ```
 
+To install the package so that it is accessible from system Python, run cmake
+with the flag `-DCMAKE_INSTALL_PYDIR` set to a directory on your PYTHONPATH and
+subsequently run `make install`.
+
 ## absl::Duration
 
 `absl::Duration` objects are converted to/ from python datetime.timedelta objects.

pybind11_abseil/CMakeLists.txt

@@ -178,3 +178,14 @@ target_link_libraries(status_casters INTERFACE import_status_module
                                                status_caster statusor_caster)
 
 add_subdirectory(tests)
+
+if(CMAKE_INSTALL_PYDIR)
+
+  install(
+    TARGETS status ok_status_singleton
+    EXPORT pybind11_abseilTargets
+    LIBRARY DESTINATION ${CMAKE_INSTALL_PYDIR}/pybind11_abseil
+    ARCHIVE DESTINATION ${CMAKE_INSTALL_PYDIR}/pybind11_abseil
+    RUNTIME DESTINATION ${CMAKE_INSTALL_PYDIR}/pybind11_abseil)
+
+endif()