cpp.texi (Obsolete Features): Add background on the origin of assertions.

	* doc/cpp.texi (Obsolete Features): Add background on the
	origin of assertions.

From-SVN: r170261

gcc/ChangeLog

+2011-02-18  Gerald Pfeifer  <gerald@pfeifer.com>
+
+	* doc/cpp.texi (Obsolete Features): Add background on the
+	origin of assertions.
+
 2011-02-17  Iain Sandoe  <iains@gcc.gnu.org>
 
 	* config/darwin-c.c (darwin_cpp_builtins): Define __OBJC2__ for

gcc/doc/cpp.texi

@@ -4200,9 +4200,10 @@ program will run on.  Assertions are usually predefined, but you can
 define them with preprocessing directives or command-line options.
 
 Assertions were intended to provide a more systematic way to describe
-the compiler's target system.  However, in practice they are just as
-unpredictable as the system-specific predefined macros.  In addition, they
-are not part of any standard, and only a few compilers support them.
+the compiler's target system and we added them for compatibility with
+existing compilers.  In practice they are just as unpredictable as the
+system-specific predefined macros.  In addition, they are not part of
+any standard, and only a few compilers support them.
 Therefore, the use of assertions is @strong{less} portable than the use
 of system-specific predefined macros.  We recommend you do not use them at
 all.