[IPO/LowerTypesTest] Skip blockaddress(es) when replacing uses.

Blockaddresses refer to the function itself, therefore replacing them
would cause an assertion in doRAUW.

Fixes https://bugs.llvm.org/show_bug.cgi?id=35201

This was found when trying CFI on a proprietary kernel by Dmitry Mikulin.

Differential Revision:  https://reviews.llvm.org/D39695

llvm-svn: 317527