Fix Issue 10523 - Enabled BigInt to work in CTFE

[davidisinta]

Added if statements to call free only at runtime so that the functions can also execute at compile time.

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[ryuukk]

Somebody should perhaps look into removing the useless allocations, that code must be very slow

[dkorpel]

I wonder if it would be better to put the __ctfe check in the implementation of GC.free, so you wouldn't need to guard every call site out there.

[davidisinta]

@dkorpel I dont think putting the __ctfe check in GC.free would work. From my understanding free is always a runtime function so that check would never return true because free can only be called in a runtime context.