[ORC] Rename MachOCompactUnwindSectionName to MachOUnwindInfoSectionName.
a1ff2d18466 should have disambiguated MachOCompactUnwindInfoSectionName to
MachOUnwindInfoSectionName, given how it's used in MachOPlatform and its
value.
A MachOCompactUnwindSectionName variable with an appropriate value will be
added in an upcoming patch to re-enable compact-unwind support in JITLink.