Create PARROT_HOT and PARROT_COLD function annotations

[petdance]

 http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html

"The hot attribute is used to inform the compiler that a function is a hot spot of the compiled program. The function is optimized more aggressively and on many target it is placed into special subsection of the text section so all hot functions appears close together improving locality."

There's also the cold attribute.

Other compilers likely have optimizations that can be used here as well.

[petdance]

r45410 adds support for PARROT_HOT and PARROT_COLD at the compiler macro level, but the headerizer does not yet support them.

[petdance]

r45411 adds support in the headerizer for PARROT_HOT and PARROT_COLD.

I welcome testing of their effect on optimization.