Add ${CMAKE_BINARY_DIR}/src/private to the introspection gir_libdirs of the two
calendar libraries. Both libecal and libedata-cal link the private
libedbus-private.dylib (install name @rpath/libedbus-private.dylib), so the
temporary binary that g-ir-scanner links and runs to dump the type info needs
src/private on its library/rpath search path to load it. Every other module
that links edbus-private (libedataserver, libebackend, libedataserverui,
libebook, libedata-book) already lists src/private here; the two calendar
modules omit it, which on macOS makes the dump binary die at runtime with
  dyld: Library not loaded: @rpath/libedbus-private.dylib
    Referenced from: .../libecal-2.0.3.dylib
    Reason: image not found
This only affects the transient build-time introspection dump binary; the
installed libraries are unchanged.

--- src/calendar/libecal/CMakeLists.txt.orig
+++ src/calendar/libecal/CMakeLists.txt
@@ -129,6 +129,7 @@
 	-I${CMAKE_SOURCE_DIR}/src/calendar
 )
 set(gir_libdirs
+	${CMAKE_BINARY_DIR}/src/private
 	${CMAKE_BINARY_DIR}/src/camel
 	${CMAKE_BINARY_DIR}/src/libedataserver
 )
--- src/calendar/libedata-cal/CMakeLists.txt.orig
+++ src/calendar/libedata-cal/CMakeLists.txt
@@ -101,6 +101,7 @@
 	-I${CMAKE_SOURCE_DIR}/src/calendar
 )
 set(gir_libdirs
+	${CMAKE_BINARY_DIR}/src/private
 	${CMAKE_BINARY_DIR}/src/camel
 	${CMAKE_BINARY_DIR}/src/libebackend
 	${CMAKE_BINARY_DIR}/src/libedataserver