Move variable declarations to fix old MSVC versions

Commit orcc/orcc@45276517f1586ba0137b43ad33fbfc1264f94ae6 introduced a
compilation error for old versions of Microsoft's MSVC. Deepayan
Bhowmik has identified two cases in orcc-native/ that violate C90
rules, where declarations follow statements in framerate_sdl.c and
native_util.c . See http://stackoverflow.com/a/13336213/1526266 .
Whilst this is fixed in the Microsoft Platform Toolset v120, this
commit provides a fix for older platform versions too.