ptxed: suppress c4244 warning on windows

The c4244 warning is triggered by some function in the xed headers.
Ignore it when building ptxed.

Change-Id: I1a6ba18e5a1092eed8531f38fe412c9aa32f643e
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>