added compiler flag for polaris

Change-Id: Ib14c14c0618982ac7b48f5bc704c04b54ff40ed9

include/hip/hcc_detail/hip_fp16.h

@@ -34,13 +34,6 @@ typedef struct __attribute__((aligned(4))){
 typedef __half half;
 typedef __half2 half2;
 
-typedef struct{
-  union{
-    float f;
-    unsigned u;
-  };
-} struct_float;
-
 /*
 Arithmetic functions
 */