fix issue open64-compiler#33 for WHIRL2llvm

1. The w2ll will crash if compile the code like that:
```
typedef struct msa_struct {
  char **aseq;
  int    alen;
  int    nseq;
} MSA;

void WriteA2M1(MSA *msa)
{
  int  pos;
  char buf[64];
  int  cpl = 60;

  buf[cpl] = '\0';
  for (pos = 0; pos < msa->alen; pos+=cpl)
  {
    strncpy(buf, &(msa->aseq[0][pos]), cpl);
  }
}

```

2. Error Log:
```
Assertion failure ../../../../osprey/ir_tools/whirl2llvm.cxx:5815:
WHIRL2llvm::STMT2llvm, intrinsic(521) not handled
```

Signed-off-by: Zhijin Zeng <[email protected]>

osprey/ir_tools/whirl2llvm.cxx

@@ -3588,7 +3588,9 @@ WHIRL2llvm::Handle_intrn_call(WN *wn) {
     case INTRN_F8COS:   func_name = "cos";     break;
     case INTRN_STRLEN:  func_name = "strlen";  break;
     case INTRN_STRCPY:  func_name = "strcpy";  break;
+    case INTRN_STRNCPY: func_name = "strncpy"; break;
     case INTRN_STRCMP:  func_name = "strcmp";  break;
+    case INTRN_STRNCMP: func_name = "strncmp"; break;
     case INTRN_MEMCPY:  func_name = "memcpy";  break;
     case INTRN_MEMSET:  func_name = "memset";  break;
     case INTRN_MEMCMP:  func_name = "memcmp";  break;
@@ -5798,7 +5800,9 @@ WHIRL2llvm::STMT2llvm(WN *wn, W2LBB *lvbb)
       case INTRN_MEMCPY:
       case INTRN_MEMSET:
       case INTRN_STRCPY:
+      case INTRN_STRNCPY:
       case INTRN_STRCMP:
+      case INTRN_STRNCMP:
       case INTRN_STRLEN:
       case INTRN_MEMCCPY:
       case INTRN_MEMMOVE: {