[libclc] [libclc][NFC] Move convert builtins from Python generator to .cl sources (PR #172634)

[Romaric Jodin via cfe-commits]

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rjodinchr wrote:

This file is not a source, it is only included. Should it have the `.inc` extension? `clc_convert_float2int.inc` is already used, but maybe we should have something to differentiate them.

https://github.com/llvm/llvm-project/pull/172634