rts: fix conflicting StgRun definitions on wasm

This commit fixes conflicting StgRun definition when building dynamic
ways of RTS for wasm in unregisterised mode.

(cherry picked from commit bef94bde)
(cherry picked from commit 6f844296)

rts/wasm/StgRun.c

 #include "Rts.h"
 
+#if !defined(USE_MINIINTERPRETER)
+
 // We directly return the same BaseReg as passed to StgRun. This is
 // fine on wasm which doesn't have SMP.
 //
@@ -19,3 +21,5 @@ StgFunPtr StgReturn(void)
 {
     return 0;
 }
+
+#endif