cmake: update minimum required MSVC version to 2013 Update 4
Currently we mix variable declarations and code, as allowed in the C99
standard. On the other hand, MSVC 2013 prior to Update 4, seems to have
problems with such code in some corner cases.
Considering it's a free update bump the requirement, and add an explicit
check in the build system. Latter of which shamelessly copied from piglit.
v2: Do not evaluate but check the MSVC variable. (Jose)
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>