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.

src/mesa/main/compiler.h

@@ -310,6 +310,18 @@ static INLINE GLuint CPU_TO_LE32(GLuint x)
 #endif
 #endif
 
+
+/**
+ * Static (compile-time) assertion.
+ * Basically, use COND to dimension an array.  If COND is false/zero the
+ * array size will be -1 and we'll get a compilation error.
+ */
+#define STATIC_ASSERT(COND) \
+   do { \
+      typedef int static_assertion_failed[(!!(COND))*2-1]; \
+   } while (0)
+
+
 #if (__GNUC__ >= 3)
 #define PRINTFLIKE(f, a) __attribute__ ((format(__printf__, f, a)))
 #else