[CodeLayout] Size-aware machine block placement (#109711) This is an implementation of a new "size-aware" machine block placement. The idea is to reorder blocks so that the number of fall-through jumps is maximized. Observe that profile data is ignored for the optimization, and it is applied only for instances with hasOptSize()=true. This strategy has two benefits: (i) it eliminates jump instructions, which results in smaller text size; (ii) we avoid using profile data while reordering blocks, which yields more "uniform" functions, thus helping ICF and machine outliner/merger. For large (mobile) apps, the size benefits of (i) and (ii) are roughly the same, combined providing up to 0.5% uncompressed and up to 1% compressed savings size on top of the current solution. The optimization is turned off by default.
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