write attributes in a header for ease of use

this handles different compilers automatically and just provides a
common method of using the attributes. Plus, it's less characters!

src/util/atrb.h

@@ -0,0 +1,49 @@
+#pragma once
+
+
+// default attribute definitions (empty)
+#define atrb_deprecated
+#define atrb_unused
+#define atrb_pure
+#define atrb_const
+#define atrb_format()
+#define atrb_nonnull()
+
+// define the attributes where possible
+#if defined(__GNUC__) || defined(__clang__)
+
+# if __has_attribute(deprecated)
+#  undef atrb_deprecated
+#  define atrb_deprecated __attribute__((deprecated))
+# endif
+
+# if __has_attribute(unused)
+#  undef atrb_unused
+#  define atrb_unused __attribute__((unused))
+# endif
+
+# if __has_attribute(pure)
+#  undef atrb_pure
+#  define atrb_pure __attribute__((pure))
+# endif
+
+
+# if __has_attribute(const)
+#  undef atrb_const
+#  define atrb_const __attribute__((const))
+# endif
+
+# if __has_attribute(format)
+#  undef atrb_format
+#  define atrb_format(...) __attribute__((format(__VA_ARGS__)))
+# endif
+
+# if __has_attribute(nonnull)
+#  undef atrb_nonnull
+#  define atrb_nonnull(...) __attribute__((nonnull(__VA_ARGS__)))
+# endif
+#elif defined(_MSC_VER)
+# undef atrb_depatrb_deprecated
+# define atrb_deprecated __declspec(deprecated)
+#endif
+