Tests/FortranModules: add test for TARGET_OBJECTS-as-linked-items module usage

Test module usage across a `$<TARGET_OBJECTS>`-as-linked-items use case.

See: #25425

Tests/FortranModules/ModulesViaSubdirTargetObjectsLink/subdir/obj.f90

@@ -0,0 +1,11 @@
+module m1
+
+implicit none
+
+contains
+
+pure real function pi()
+pi = 4*atan(1.)
+end function
+
+end module m1