This change adds the CMake option;

  ENABLE_STATIC_CRT  Build libnghttp2 against the MS LIBCMT[d]

This avoids linking to msvcrt.lib for binaries to compile (/MT[d])
and link against the static C Runtime libcrt.lib, and
avoiding the msvcrt[d].dll dependency.
Signed-off-by: William A Rowe Jr <wrowe@pivotal.io>
Signed-off-by: Yechiel Kalmenson <ykalmenson@pivotal.io>