c++config (__USE_MALLOC): Report case where the user improperly defined it on the command line.

	libstdc++/6641
	* include/bits/c++config (__USE_MALLOC): Report case where
	the user improperly defined it on the command line.

From-SVN: r53494

libstdc++-v3/ChangeLog

+2002-05-15  Loren J. Rittle <ljrittle@acm.org>
+
+	libstdc++/6641
+	* include/bits/c++config (__USE_MALLOC): Report case where
+	the user improperly defined it on the command line.
+
 2002-05-15  Rainer Orth  <ro@TechFak.Uni-Bielefeld.DE>
 
 	* testsuite/testsuite_hooks.h (__set_testsuite_memlimit):

libstdc++-v3/include/bits/c++config

@@ -69,7 +69,15 @@
 // that threads are properly configured on your platform before
 // assigning blame to the STL container-memory allocator.  After doing
 // so, please report any possible issues to libstdc++@gcc.gnu.org .
-// Do not blindly #define __USE_MALLOC here or on the command line.
+// Do not define __USE_MALLOC on the command line.  Enforce it here:
+#ifdef __USE_MALLOC
+#error __USE_MALLOC should only be defined within \
+libstdc++-v3/include/bits/c++config before full recompilation of the library.
+#endif
+// Define __USE_MALLOC after this point in the file in order to aid debugging
+// or globally change allocation policy.  This breaks the ABI, thus
+// completely recompile the library.  A patch to better support
+// changing the global allocator policy would be probably be accepted.
 
 // The remainder of the prewritten config is mostly automatic; all the
 // user hooks are listed above.