glibc: add eglibc 2.19-svnr25243 and choice menu

Add glibc 2.19-svnr25243 and a choice menu to select between different
eglibc versions.
Blacklist it for PowerPC SPE since it doesn't even build.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>