bad procedure entry masks in bcmp, bcopy, bzero

[Dave Martindale]

Bcmp, bcopy, bzero, and any other C library routines conform to C calling
conventions even though they are written in assembler.  Registers r0-r5
are never saved because they are always scratch registers in C code;
this saves time on routine call and return.  If you write in assembler
and call C routines and expect r0-r5 to be preserved, you have to do it
yourself.  This IS a feature, not a bug.