compiler-rt: Rename .cc files in lib/interception to .cpp.

See https://reviews.llvm.org/D58620 for discussion, and for the commands
I ran. In addition I also ran

  for f in $(svn diff | diffstat | grep .cc | cut -f 2 -d ' '); do rg $f . ; done

and manually updated references to renamed files found by that.

llvm-svn: 367456