add VectorSet macro

VectorSet(a,b,c,d) -> vec3_t d = (a, b, c)

This should be useful.

include/QF/mathlib.h

@@ -99,6 +99,12 @@ extern const vec_t * const vec3_origin;
 
 #define VectorIsZero(a) (!(a)[0] && !(a)[1] && !(a)[2])
 #define VectorZero(a) ((a)[2] = (a)[1] = (a)[0] = 0);
+#define VectorSet(a,b,c,d) \
+	do { \
+		(d)[0] = a; \
+		(d)[1] = b; \
+		(d)[2] = c; \
+	} while (0)
 
 #define VectorBlend(v1,v2,b,v) \
 	do { \