[mm] Disable HAVE_GNU_LD code in order to get rid of the junkarea

[mm] Disable HAVE_GNU_LD code in order to get rid of the junkarea

The HAVE_GNU_LD mode of mmalloc delegates in some cases to standard
malloc()/free() which are resolved with dlsym(). This cause some
bootstrap problems which are only resolved with the junkarea: the
junkarea is regularly broken when adding dependencies because the
junkarea is then too small.

By disabling the HAVE_GNU_LD path, we get rid of the junkarea hack.