ARM: Fix GCC 7 -Wimplicit-fallthrough warnings.

src/lj_asm.c

@@ -1719,8 +1719,8 @@ static void asm_setup_regsp(ASMState *as)
 #if LJ_SOFTFP
     case IR_MIN: case IR_MAX:
       if ((ir+1)->o != IR_HIOP) break;
-      /* fallthrough */
 #endif
+    /* fallthrough */
     /* C calls evict all scratch regs and return results in RID_RET. */
     case IR_SNEW: case IR_XSNEW: case IR_NEWREF:
       if (REGARG_NUMGPR < 3 && as->evenspill < 3)

src/lj_asm_arm.h

@@ -1046,7 +1046,7 @@ static ARMIns asm_fxloadins(IRIns *ir)
   case IRT_I16: return ARMI_LDRSH;
   case IRT_U16: return ARMI_LDRH;
   case IRT_NUM: lua_assert(!LJ_SOFTFP); return ARMI_VLDR_D;
-  case IRT_FLOAT: if (!LJ_SOFTFP) return ARMI_VLDR_S;
+  case IRT_FLOAT: if (!LJ_SOFTFP) return ARMI_VLDR_S;  /* fallthrough */
   default: return ARMI_LDR;
   }
 }
@@ -1057,7 +1057,7 @@ static ARMIns asm_fxstoreins(IRIns *ir)
   case IRT_I8: case IRT_U8: return ARMI_STRB;
   case IRT_I16: case IRT_U16: return ARMI_STRH;
   case IRT_NUM: lua_assert(!LJ_SOFTFP); return ARMI_VSTR_D;
-  case IRT_FLOAT: if (!LJ_SOFTFP) return ARMI_VSTR_S;
+  case IRT_FLOAT: if (!LJ_SOFTFP) return ARMI_VSTR_S;  /* fallthrough */
   default: return ARMI_STR;
   }
 }