[flang][msvc] Fix lambda capture ambiguity. NFC.

Patch D88695 introduces a new local variable inside a lambda with the same name as a variable outside of it. In some of the if constexpr regions, msvc prioritizes the outer declaration and emits the error.
```
C:\Users\meinersbur\src\llvm-project\flang\lib\Evaluate\fold-implementation.h(1200): error C3493: 'context' cannot be implicitly captured because no default capture mode has been specified
```

This is fixed by giving the inner variable a different name.

Reviewed By: klausler

Differential Revision: https://reviews.llvm.org/D89367

flang/lib/Evaluate/fold-implementation.h

@@ -1185,24 +1185,24 @@ Expr<TO> FoldOperation(
         auto &convert{msvcWorkaround.convert};
         char buffer[64];
         if (auto value{GetScalarConstantValue<Operand>(kindExpr)}) {
-          FoldingContext &context{msvcWorkaround.context};
+          FoldingContext &ctx{msvcWorkaround.context};
           if constexpr (TO::category == TypeCategory::Integer) {
             if constexpr (Operand::category == TypeCategory::Integer) {
               auto converted{Scalar<TO>::ConvertSigned(*value)};
               if (converted.overflow) {
-                context.messages().Say(
+                ctx.messages().Say(
                     "INTEGER(%d) to INTEGER(%d) conversion overflowed"_en_US,
                     Operand::kind, TO::kind);
               }
               return ScalarConstantToExpr(std::move(converted.value));
             } else if constexpr (Operand::category == TypeCategory::Real) {
               auto converted{value->template ToInteger<Scalar<TO>>()};
               if (converted.flags.test(RealFlag::InvalidArgument)) {
-                context.messages().Say(
+                ctx.messages().Say(
                     "REAL(%d) to INTEGER(%d) conversion: invalid argument"_en_US,
                     Operand::kind, TO::kind);
               } else if (converted.flags.test(RealFlag::Overflow)) {
-                context.messages().Say(
+                ctx.messages().Say(
                     "REAL(%d) to INTEGER(%d) conversion overflowed"_en_US,
                     Operand::kind, TO::kind);
               }
@@ -1215,17 +1215,17 @@ Expr<TO> FoldOperation(
                 std::snprintf(buffer, sizeof buffer,
                     "INTEGER(%d) to REAL(%d) conversion", Operand::kind,
                     TO::kind);
-                RealFlagWarnings(context, converted.flags, buffer);
+                RealFlagWarnings(ctx, converted.flags, buffer);
               }
               return ScalarConstantToExpr(std::move(converted.value));
             } else if constexpr (Operand::category == TypeCategory::Real) {
               auto converted{Scalar<TO>::Convert(*value)};
               if (!converted.flags.empty()) {
                 std::snprintf(buffer, sizeof buffer,
                     "REAL(%d) to REAL(%d) conversion", Operand::kind, TO::kind);
-                RealFlagWarnings(context, converted.flags, buffer);
+                RealFlagWarnings(ctx, converted.flags, buffer);
               }
-              if (context.flushSubnormalsToZero()) {
+              if (ctx.flushSubnormalsToZero()) {
                 converted.value = converted.value.FlushSubnormalToZero();
               }
               return ScalarConstantToExpr(std::move(converted.value));