Fix malloc_info namespace (bug 17570).

Fix malloc_info namespace (bug 17570).

malloc_info is defined in the same file as malloc and free, but is not
an ISO C function, so should be a weak symbol.  This patch makes it
so.

Tested for x86_64 (testsuite, and that disassembly of installed shared
libraries is unchanged by the patch).

	[BZ #17570]
	* malloc/malloc.c (malloc_info): Rename to __malloc_info and
	define as weak alias of __malloc_info.