[RuntimeDyld] Fix resolving R_PPC64_REL24 relocations

When resolving R_PPC64_REL24, code used to check for an address delta
that fits in 24 bits, while the instructions that take this relocation
actually can process address deltas that fit into *26* bits (as those
instructions have a 24 bit field, but implicitly append two zero bits
at the end since all instruction addresses are a multiple of 4).

This means that code would signal overflow once a single object's text
section exceeds 8 MB, while we can actually support up to 32 MB.

Partially fixes PR25540.

llvm-svn: 253369