mesa: add STATIC_ASSERT() macro for compile-time assertions

mesa: add STATIC_ASSERT() macro for compile-time assertions

This can be used to check that tables have the right number of entries,
etc. at compile-time.  This will hopefully catch things that are missed
if particular drivers aren't tested, for example.

v2: Simplify the macro to omit the extra line number info (the compiler
already indicates the line number).  And wrap the macro for readability.