[PowerPC] Add BCDCOPYSIGN and BCDSETSIGN Instruction Support (#144874)

Support the following BCD format conversion builtins for PowerPC.

- `__builtin_bcdcopysign` – Conversion that returns the decimal value of
the first parameter combined with the sign code of the second parameter.
`
- `__builtin_bcdsetsign` – Conversion that sets the sign code of the
input parameter in packed decimal format.

> Note: This built-in function is valid only when all following
conditions are met:
> -qarch is set to utilize POWER9 technology.
> The bcd.h file is included.

## Prototypes

```c
vector unsigned char __builtin_bcdcopysign(vector unsigned char, vector unsigned char);
vector unsigned char __builtin_bcdsetsign(vector unsigned char, unsigned char);
```

## Usage Details

`__builtin_bcdsetsign`: Returns the packed decimal value of the first
parameter combined with the sign code.
The sign code is set according to the following rules:
- If the packed decimal value of the first parameter is positive, the
following rules apply:
     - If the second parameter is 0, the sign code is set to 0xC.
     - If the second parameter is 1, the sign code is set to 0xF.
- If the packed decimal value of the first parameter is negative, the
sign code is set to 0xD.
> notes:
>     The second parameter can only be 0 or 1.
> You can determine whether a packed decimal value is positive or
negative as follows:
> - Packed decimal values with sign codes **0xA, 0xC, 0xE, or 0xF** are
interpreted as positive.
> - Packed decimal values with sign codes **0xB or 0xD** are interpreted
as negative.

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Co-authored-by: Aditi-Medhane <aditi.medhane@ibm.com>