scons: Don't use bundled C99 headers for VS 2013.

Use the ones provided by the compiler instead.

NOTE: External trees should be updated to not include '#include/c99'
directory directly, but rather rely on scons/gallium.py to do the right
thing.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
2 files changed