libc/uClibc: add additional debug level between "minimal" and "all"

During application development it is desirable to enable malloc
debugging and LD_DEBUG support, but the extensive debug spew from
SUPPORT_LD_DEBUG_EARLY is only useful when working on
uClibc's ld.so.

Signed-off-by: Johannes Stezenbach <js@sig21.net>

 reporter_name="Gustavo Zacarias <gustavo@zacarias.com.ar>"

 reporter_url="http://sourceware.org/ml/crossgcc/2011-03/msg00028.html"

 reporter_comment=""