Rename stdnoreturn.h to helpers.h

This file will contain more compiler-specific helpers.

Signed-off-by: Antonio Niño Díaz <antonio_nd@outlook.com>

include/helpers.h

@@ -0,0 +1,38 @@
+/*
+ * This file is part of RGBDS.
+ *
+ * Copyright (c) 2014-2018, RGBDS contributors.
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#ifndef HELPERS_H
+#define HELPERS_H
+
+#if defined(__STDC_VERSION__)
+	#if __STDC_VERSION__ >= 201112L
+		/* C11 or newer */
+		#define noreturn _Noreturn
+	#endif
+#endif
+
+#if defined(__GNUC__) && !defined(noreturn)
+	#if __GNUC__ > 2 || (__GNUC__ == 2 && (__GNUC_MINOR__ >= 5))
+		/* GCC 2.5 or newer */
+		#define noreturn __attribute__ ((noreturn))
+	#endif
+#endif
+
+#if defined(_MSC_VER) && !defined(noreturn)
+	#if _MSC_VER >= 1310
+		/* MS Visual Studio 2003/.NET Framework 1.1 or newer */
+		#define noreturn _declspec(noreturn)
+	#endif
+#endif
+
+#if !defined(noreturn)
+	/* Unsupported, but no need to throw a fit */
+	#define noreturn
+#endif
+
+#endif /* HELPERS_H */