MdePkg: avoid __builtin_unreachable() on GCC v4.4
MdePkg: avoid __builtin_unreachable() on GCC v4.4

GCC v4.4 does not implement __builtin_unreachable(), so avoid using
it when building with this version or earlier.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <66d3c5fdaeea7ff1f996ad04f2c45e08ab38e2f5@linaro.org>
Reviewed-by: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>
Tested-by: Laszlo Ersek <7437296077edea1cb64451c122c4dac071f0cfbc@redhat.com>
Tested-By: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>
Reviewed-by: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>

MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2,MattDevo/edk2