[compiler-rt] [ubsan] Fix printing of floats in mingw mode

In mingw mode on x86, long doubles are 80 bit - while MSVC mode uses
long doubles that are equal to regular doubles (on all architectures).

In the case of this formatting function, we're calling a MS CRT
provided printf function which interprets long doubles as 64 bit.

Since the long doubles are equal to regular doubles on all MSVC
platforms, just use regular double formatting. For MSVC environments
there's no difference, but for mingw environments, this avoids the
ambiguity.

Differential Revision: https://reviews.llvm.org/D148133