Fix linking error by making a inline function static

See: bootchk/resynthesizer#100

Undefined symbols for architecture x86_64:
  "_swap_vector_elements", referenced from:
      _orderTargetPointsRandom in libresynthesizer.a(engine.c.o)
      _randomizeBandsTargetPoints in libresynthesizer.a(engine.c.o)
ld: symbol(s) not found for architecture x86_64

resynthesizer/engineTypes.h

@@ -228,7 +228,7 @@ get_center (
 
 
 /* swap two elements of a point vector */
-inline void
+static inline void
 swap_vector_elements(
   pointVector vector,
   guint size,