BLD: Add a pkgconfig file (xtensor-stack#310)

Similar to xtensor-stack/xtensor-blas#243 and
done for the same reason (easier to integrate with `meson`).

Author: HaoZeke

CMakeLists.txt

@@ -124,6 +124,12 @@ export(EXPORT ${PROJECT_NAME}-targets
 install(FILES ${XTENSOR_PYTHON_HEADERS}
         DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/xtensor-python)
 
+configure_file(${PROJECT_NAME}.pc.in
+               "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
+                @ONLY)
+install(FILES "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
+        DESTINATION "${CMAKE_INSTALL_DATADIR}/pkgconfig/")
+
 set(XTENSOR_PYTHON_CMAKECONFIG_INSTALL_DIR "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}" CACHE
     STRING "install path for xtensor-pythonConfig.cmake")
 

xtensor-python.pc.in

@@ -0,0 +1,7 @@
+prefix=@CMAKE_INSTALL_PREFIX@
+includedir=${prefix}/include
+
+Name: xtensor-python
+Description: An extension to the xtensor library, offering Python bindings with enhanced NumPy support.
+Version: @xtensor-python_VERSION@
+Cflags: -I${includedir}