[flang][NFC] simplify dispatching of reduction runtime calls (#110479)

As part of t[he RFC to replace fir.complex usages by mlir
complex](https://discourse.llvm.org/t/rfc-flang-replace-usages-of-fir-complex-by-mlir-complex-type/82292),
this patch updates the type dispatch in Reduction.cpp to use macros to
avoid naming the types everywhere and to avoid typos when copy-pasting
the if/else chains.

Author: jeanPerier

flang/include/flang/Optimizer/Support/Utils.h

@@ -185,6 +185,10 @@ mlirTypeToCategoryKind(mlir::Location loc, mlir::Type type) {
     return {Fortran::common::TypeCategory::Complex, complexType.getFKind()};
   else if (auto logicalType = mlir::dyn_cast<fir::LogicalType>(type))
     return {Fortran::common::TypeCategory::Logical, logicalType.getFKind()};
+  else if (auto charType = mlir::dyn_cast<fir::CharacterType>(type))
+    return {Fortran::common::TypeCategory::Character, charType.getFKind()};
+  else if (mlir::isa<fir::RecordType>(type))
+    return {Fortran::common::TypeCategory::Derived, 0};
   else
     fir::emitFatalError(loc,
                         "unsupported type: " + fir::mlirTypeToString(type));