[llvm] DAG: Add RTLIB::getPOW helper (PR #147274)

[Paul Walker via llvm-commits]

================
@@ -723,6 +718,9 @@ SDValue DAGTypeLegalizer::SoftenFloatRes_ExpOp(SDNode *N) {
                              : RTLIB::getLDEXP(N->getValueType(0));
   assert(LC != RTLIB::UNKNOWN_LIBCALL && "Unexpected fpowi.");
   if (!TLI.getLibcallName(LC)) {
+    RTLIB::Libcall NewLC = RTLIB::getPOW(N->getValueType(0));
+    assert(NewLC != RTLIB::UNKNOWN_LIBCALL);
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paulwalker-arm wrote:

```suggestion
    assert(NewLC != RTLIB::UNKNOWN_LIBCALL && "Unexpected fpow.");
```

https://github.com/llvm/llvm-project/pull/147274