configure: Eliminate MSVC2008 compatibility.

configure: Eliminate MSVC2008 compatibility.

We no longer need to build any part of Mesa with Windows SDK 7.0.7600 or
MSVC 2008.  MSVC 2013 will be the oldest we support.

In practice this means people are now free to declare variables in the
middle of blocks, on the whole Mesa tree.

Care should still be taken with variable length arrays and void pointer
arithmetic.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Hella-acked-by: Ian Romanick <ian.d.romanick@intel.com>