[support] Temporarily disable Inf/NaN testing in PrintNumber

This is still breaking on some platforms. The underlying implementation
doesn't seem to be the cause, rather the test is not robust across
platforms. So, we'll just disable this for the time being, to unblock
builds until we have a proper fix.

Reviewed By: abhina.sreeskantharajan

Differential Revision: https://reviews.llvm.org/D146834