[flang] Allow derf as alternate spelling for erf (llvm#95784)

This patch adds derf as an alternate spelling for the erf intrinsic.
This spelling is supported by multiple other compilers and used by WRF.

Author: DavidTruby

flang/lib/Evaluate/intrinsics.cpp

@@ -1113,6 +1113,7 @@ static const SpecificIntrinsicInterface specificIntrinsicFunction[]{
     {{"ddim", {{"x", DoublePrecision}, {"y", DoublePrecision}},
          DoublePrecision},
         "dim"},
+    {{"derf", {{"x", DoublePrecision}}, DoublePrecision}, "erf"},
     {{"dexp", {{"x", DoublePrecision}}, DoublePrecision}, "exp"},
     {{"dfloat", {{"a", AnyInt}}, DoublePrecision}, "real", true},
     {{"dim", {{"x", DefaultReal}, {"y", DefaultReal}}, DefaultReal}},

flang/unittests/Evaluate/intrinsics.cpp

@@ -344,6 +344,7 @@ void TestIntrinsics() {
   TEST(table.GetGenericIntrinsicName("dcos") == "cos");
   TEST(table.GetGenericIntrinsicName("dcosh") == "cosh");
   TEST(table.GetGenericIntrinsicName("ddim") == "dim");
+  TEST(table.GetGenericIntrinsicName("derf") == "erf");
   TEST(table.GetGenericIntrinsicName("dexp") == "exp");
   TEST(table.GetGenericIntrinsicName("dint") == "aint");
   TEST(table.GetGenericIntrinsicName("dlog") == "log");