SmallerC: generate smaller & faster code; bugfixes
Improvements:
- use registers more efficiently
- eliminate some register copies and stack manipulations
- promote left operands to right immediate operands
- improve simple assignments to auto/static vars
- use bltz, blez, bgtz, bgez
- change mul/divu (by powers of 2) to sll/srl/and
- use seb, seh for sign extension instead of sll/sra
- overall generate a bit tighter, faster and more readable asm code

Fixes:
- >>= should be unsigned when the left operand is unsigned int.
The right operand isn't important here.
- very subtle bug in e.g. void f(){int a; &a+1;/*wrong value of &a+1*/}

Other:
- include stdarg.c and skeleton.c in /share/example/Makefile
Merge branch 'master' of https://github.com/alexfru/retrobsd
Merge pull request #41 from alexfru/master

SmallerC: generate smaller & faster code; bugfixes