Cast C enumerators used as shift counts to int

[unsafePtr]

In C an enumerator has type int, so a shift by one takes the "already the correct type" case in VisitBinaryOperator and is written bare. The generator emits the enumerator as a member of its C# enum, though, and C# cannot shift by an enum:

enum Bits { BIT_A };
#define FLAG_A (1U << BIT_A)

// error CS0019: Operator '<<' cannot be applied to operands of type 'uint' and 'Bits'
public const uint FLAG_A = (1U << BIT_A);

In C++ the enumerator has the enum's type and already falls through to the (int)(...) fallback, so only C is affected. This adds a case ahead of the int case that casts when the shift count, as written (ignoring parentheses and implicit casts), is a reference to an enumerator. The new EnumConstantBitshiftTest sits next to UnsignedIntBitshiftTest from #611 and covers a constant and a macro, each with and without parentheses; it fails without the change (FlagA = 1U << BIT_A;).

Found while generating bindings for Linux's io_uring.h, whose IOSQE_* flags are defined as (1U << IOSQE_*_BIT).

Testing: the full ClangSharp.PInvokeGenerator.UnitTests suite passes on Windows. With RUN_ALL_VARIANTS=1 the only failures are 16 in WideStringLiteralConstTest and WideStringLiteralStaticConstTest, which fail the same way on main when the Unix variants run on a Windows host.

🤖 Generated with Claude Code