[CodeGen] Enable processing of interconnected complex number operations

[CodeGen] Enable processing of interconnected complex number operations

With this patch, ComplexDeinterleavingPass now has the ability to handle
any number of interconnected operations involving complex numbers.
For example, the patch enables the processing of code like the following:

for (int i = 0; i < 1000; ++i) {
    a[i] =  w[i] * v[i];
    b[i] =  w[i] * u[i];
}

This code has multiple arrays containing complex numbers and a common
subexpression `w` that appears in two expressions.

Differential Revision: https://reviews.llvm.org/D146988