Add initial support for 'goto' statements.

ispc now supports goto, but only under uniform control flow--i.e.
it must be possible for the compiler to statically determine that
all program instances will follow the goto.  An error is issued at
compile time if a goto is used when this is not the case.

examples/intrinsics/generic-16.h

@@ -307,6 +307,12 @@ static FORCEINLINE uint32_t __movmsk(__vec16_i1 mask) {
     return mask.v;
 }
 
+static FORCEINLINE __vec16_i1 __equal(__vec16_i1 a, __vec16_i1 b) {
+    __vec16_i1 r;
+    r.v = (a.v & b.v) | (~a.v & ~b.v);
+    return r;
+}
+
 static FORCEINLINE __vec16_i1 __and(__vec16_i1 a, __vec16_i1 b) {
     __vec16_i1 r;
     r.v = a.v & b.v;