uclibc-snapshot: enable option UCLIBC_SUSV2_LEGACY

With uClibc commit e8065705, valloc is now optional in SUSv2 and removed
from SUSv3 and later. However, cdrkit currently requires valloc, so
enable it in the uClibc snapshot configuration file.

Fixes
http://autobuild.buildroot.net/results/5a5/5a51f3f06e04eed39d59477ea1178aef7d397754/



Signed-off-by: Chris Zankel <chris@zankel.net>
[baruch: fix summary line, add autobuild reference]
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>