Minor optimizations about gmqcc HOT 4 CLOSED

First part done. Second part: better allocation of temps in general and overlapping them with locals. This requires some more thought though.

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The correct name for these optimizations is called "peephole optimization", not "minor optimization". Please call them as such :)

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It's more than just that. Eg. -Ominor should also use the space of explicitly declared local variables as temps when they're not required for anything else. ie:

void foo(float cond) {
    float a, b;
    if (cond) {
        a = get();
        return a * 3 + a * a; // 'b' is entirely unused in this block so one of the MULs is stored in 'b'
    } else {
        a = get();
        b = get();
        return a + b;
    }
}

Closing for now. The "wasted space after temps" is fixed; -Opeephole reduces code size bout some 3%, and -Otail-recursion works fine too. Other optimizations come in 0.3.

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