* src/SDCCpeeph.c (labelIsReturnOnly): support hc08 rts opcode also

* src/SDCCpeeph.c (labelIsReturnOnly): support hc08 rts opcode also
* src/SDCCpeeph.c (buildLabelRefCountHash): assume function entry point
labels are referenced at least once (even if a reference is not found)
* src/hc08/gen.c (emitcode): set isComment flag for comments
* src/hc08/peeph.def: added rules 5a..5f (optimize redundant immediate
loads), rules 6a..6b (optimize jumps to return)

git-svn-id: https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc@3466 4a8a32a2-be11-0410-ad9d-d568d2c75423