Include source position of broken docs.

Some source code included "{@link }" which broke the @SystemApi docs
build with a useless error message.  This change adds logging to
identify the source position.

Test: make -j32 online-system-api-sdk-docs
Bug: 38164929
Change-Id: Idcf2ba68daa904584e2f2c3daf6228bc25e651d7
2 files changed