fixup: MSVC __builtin_expect shim for the cold-path hints

Windows MSVC build of upstream PR #4949 failed with
`LNK2019: unresolved external symbol __builtin_expect` because
`__builtin_expect` is a GCC/Clang builtin and MSVC has nothing
equivalent. The branch-predictor hints are an optimization, not
correctness, so the simplest portable fix is a no-op fallback
gated on `!defined(__GNUC__) && !defined(__clang__)`.

Lives at the top of `wasm_interp_fast.c` rather than in
`bh_platform.h` to avoid touching the shared header for a
local cold-path concern.

Author: matthargett

core/iwasm/interpreter/wasm_interp_fast.c

@@ -25,6 +25,15 @@
 #include "simde/wasm/simd128.h"
 #endif
 
+/* MSVC has no `__builtin_expect`; the cold-path hints below are
+ * GCC/Clang only. Provide a no-op fallback so the loop still
+ * compiles on the Windows MSVC build. Branch-predictor hints are
+ * an optimization, not correctness, so dropping them on MSVC is
+ * fine. */
+#if !defined(__GNUC__) && !defined(__clang__)
+#define __builtin_expect(expr, expected) (expr)
+#endif
+
 typedef int32 CellType_I32;
 typedef int64 CellType_I64;
 typedef float32 CellType_F32;