Fix #4225

[Kelimion]

Fixes #4225. Turns compiler assert into:

W:/Odin/bug/bug.odin(6:26) Error: Cannot cast '42.1' as 'u64' from 'untyped float' 
	v := transmute(i64)(u64(42.1)) 
	                        ^~~^ 
	42.100000 cannot be represented without truncation/rounding as the type 'u64' 

[galt-john]

Great diagnosis Jeroen and wonderful error message. Thank you!

[Kelimion]

Just commenting out the assert also works, so it could be that it's a remnant from before the inexact error message was added. I leave this to @gingerBill to decide which approach is better here.