Fix ambiguity in const parsing

include/asm/constexpr.h

@@ -0,0 +1,33 @@
+/*
+ * This file is part of RGBDS.
+ *
+ * Copyright (c) 1997-2018, Carsten Sorensen and RGBDS contributors.
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#ifndef RGBDS_ASM_CONSTEXPR_H
+#define RGBDS_ASM_CONSTEXPR_H
+
+#include <stdint.h>
+
+struct ConstExpression {
+	union {
+		int32_t nVal;
+		struct sSymbol *pSym;
+	} u;
+	uint32_t isSym;
+};
+
+void constexpr_Symbol(struct ConstExpression *expr, char *tzSym);
+void constexpr_Number(struct ConstExpression *expr, int32_t i);
+void constexpr_UnaryOp(struct ConstExpression *expr,
+		       int32_t op,
+		       const struct ConstExpression *src);
+void constexpr_BinaryOp(struct ConstExpression *expr,
+			int32_t op,
+			const struct ConstExpression *src1,
+			const struct ConstExpression *src2);
+int32_t constexpr_GetConstantValue(struct ConstExpression *expr);
+
+#endif /* RGBDS_ASM_CONSTEXPR_H */