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="Thomas Petazzoni"

reporter_url="http://www.free-electrons.com/"

reporter_comment="Very basic testing only"