Added a BOOST_DEPRECATED macro for deprecated symbol markup.

BOOST_DEPRECATED can be used to mark functions, types and objects as
deprecated, with a message with a recommendation of replacement. Using
such marked symbols in code will generate compiler warnings, with the
specified message, if possible.

The warnings can be suppressed if BOOST_ALLOW_DEPRECATED_SYMBOLS is defined.
Additionally, added support BOOST_ALLOW_DEPRECATED macro that not only
allows for deprecated symbols but also deprecated headers (i.e. defining
BOOST_ALLOW_DEPRECATED is equivalent to defining both
BOOST_ALLOW_DEPRECATED_SYMBOLS and BOOST_ALLOW_DEPRECATED_HEADERS).

include/boost/config/compiler/clang.hpp

@@ -325,11 +325,18 @@
 // All versions with __cplusplus above this value seem to support this:
 #  define BOOST_NO_CXX14_DIGIT_SEPARATORS
 #endif
-//
-// __builtin_unreachable:
-#if defined(__has_builtin) && __has_builtin(__builtin_unreachable)
+
+// Unreachable code markup
+#if defined(__has_builtin)
+#if __has_builtin(__builtin_unreachable)
 #define BOOST_UNREACHABLE_RETURN(x) __builtin_unreachable();
 #endif
+#endif
+
+// Deprecated symbol markup
+#if __has_attribute(deprecated)
+#define BOOST_DEPRECATED(msg) __attribute__((deprecated(msg)))
+#endif
 
 #if (__clang_major__ == 3) && (__clang_minor__ == 0)
 // Apparently a clang bug:

include/boost/config/compiler/gcc.hpp

@@ -340,12 +340,18 @@
 // Type aliasing hint. Supported since gcc 3.3.
 #define BOOST_MAY_ALIAS __attribute__((__may_alias__))
 
-//
-// __builtin_unreachable:
+// Unreachable code markup
 #if BOOST_GCC_VERSION >= 40500
 #define BOOST_UNREACHABLE_RETURN(x) __builtin_unreachable();
 #endif
 
+// Deprecated symbol markup
+#if BOOST_GCC_VERSION >= 40500
+#define BOOST_DEPRECATED(msg) __attribute__((deprecated(msg)))
+#else
+#define BOOST_DEPRECATED(msg) __attribute__((deprecated))
+#endif
+
 #ifndef BOOST_COMPILER
 #  define BOOST_COMPILER "GNU C++ version " __VERSION__
 #endif
@@ -359,7 +365,7 @@
 
 // versions check:
 // we don't know gcc prior to version 3.30:
-#if (BOOST_GCC_VERSION< 30300)
+#if (BOOST_GCC_VERSION < 30300)
 #  error "Compiler not configured - please reconfigure"
 #endif
 //

include/boost/config/compiler/sunpro_cc.hpp

@@ -86,6 +86,12 @@
 #  define BOOST_SYMBOL_VISIBLE __global
 #endif
 
+// Deprecated symbol markup
+// Oracle Studio 12.4 supports deprecated attribute with a message; this is the first release that supports the attribute.
+#if (__SUNPRO_CC >= 0x5130)
+#define BOOST_DEPRECATED(msg) __attribute__((deprecated(msg)))
+#endif
+
 #if (__SUNPRO_CC < 0x5130)
 // C++03 features in 12.4:
 #define BOOST_NO_TWO_PHASE_NAME_LOOKUP

include/boost/config/compiler/visualc.hpp

@@ -107,6 +107,14 @@
 #  define BOOST_NO_RTTI
 #endif
 
+// Deprecated symbol markup
+#if (_MSC_VER >= 1400)
+#define BOOST_DEPRECATED(msg) __declspec(deprecated(msg))
+#else
+// MSVC 7.1 only supports the attribute without a message
+#define BOOST_DEPRECATED(msg) __declspec(deprecated)
+#endif
+
 //
 // TR1 features:
 //

include/boost/config/compiler/xlcpp.hpp

@@ -270,6 +270,10 @@
 #  define BOOST_NO_CXX14_DIGIT_SEPARATORS
 #endif
 
+// Deprecated symbol markup
+#if __has_attribute(deprecated)
+#define BOOST_DEPRECATED(msg) __attribute__((deprecated(msg)))
+#endif
 
 // Unused attribute:
 #if defined(__GNUC__) && (__GNUC__ >= 4)