On PowerPC, Clang uses the wrong mul/div functions for `__float128 _Complex`

[beetrees]

On PowerPC, Clang will miscompile the following code (compiler explorer):

__float128 _Complex mul_f128(__float128 _Complex a, __float128 _Complex b) {
    return a * b;
}

__ibm128 _Complex mul_ibm(__ibm128 _Complex a, __ibm128 _Complex b) {
    return a * b;
}

__float128 _Complex div_f128(__float128 _Complex a, __float128 _Complex b) {
    return a / b;
}

__ibm128 _Complex div_ibm(__ibm128 _Complex a, __ibm128 _Complex b) {
    return a / b;
}

GCC correctly uses the __mulkc3/__divkc3 functions for __float128 and the __multc3/__divtc3 functions for __ibm128, whereas Clang uses __multc3/__divtc3 for both.