minor tweak to profiled code

[Stephen Weeks]

> Just  to  make  the profiling assembler output a bit more readable, can't all
> the xxx$$End symbols that have no code (only alignment) between them and  the
> next   xxx$$Begin   be  eliminated?   Wouldn't  this  speed  up  mlprof,  and
> compilation under profiling?  In a test program, the .S file went  from  9009
> lines and 310K to 7175 lines and 205K be eliminating the $$End lines.

I talked about this with Matthew, and he pointed out that mlprof isn't even
looking for $$End labels at all, so we can just remove them entirely.  I've
made the appropriate change to x86.fun.