PR pending https://github.com/espeak-ng/espeak-ng/pull/2394.patch
cmake: use libdir to install .pc
--- a/cmake/package.cmake
+++ b/cmake/package.cmake
@@ -31,5 +31,5 @@ configure_file(
 )
 
 install(
-  FILES ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc DESTINATION lib/pkgconfig
-)
\ No newline at end of file
+  FILES ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig
+)