Don't use `addsat()`/`subsat()`; that'll erroneously flag cases where
the sum is exactly the maximum integer value, or the difference is
exactly 0. Also, correct the condition for the `select()` function; it's
basically `mix()` with a boolean factor.
(What was I *thinking*?)
Support flattening StorageOutput & StorageInput matrices and arrays.
No longer move matrix & array inputs to separate buffer.
Add separate SPIRFunction::fixup_statements_in & SPIRFunction::fixup_statements_out
instead of just SPIRFunction::fixup_statements.
Emit SPIRFunction::fixup_statements at beginning of functions.
CompilerMSL track vars_needing_early_declaration.
Pass global output variables as variables to functions that access them.
Sort input structs by location, same as output structs.
Emit struct declarations in order output, input, uniforms.
Regenerate reference shaders to new formats defined by above.
