[support] Attempt to fix PrintNumber test for Solaris

NaN and Inf are still causing some problems in a formatting test.
This patch makes the checked format string exactly match the internal
JSON format string. If there are still problems, we should disable
testing Inf and NaN values until we can come to a portable solution.

Reviewed By: abhina.sreeskantharajan

Differential Revision: https://reviews.llvm.org/D146818