[InstCombine] ctpop(X) ^ ctpop(Y) & 1 --> ctpop(X^Y) & 1 (PR50094)

Original pattern: (__builtin_parity(x) ^ __builtin_parity(y))

LLVM rewrites it as: (__builtin_popcount(x) ^ __builtin_popcount(y)) & 1

Optimized form:  __builtin_popcount(X^Y) & 1

Alive proof: https://alive2.llvm.org/ce/z/-GdWFr

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D101802