configure: do not require svn

svn is needed to download eglibc from the upstream repository.
In some situations, though, it can happen that:
- the developpers' machines do not have svn
- a LAN mirror has been set-up with pre-downloaded eglibc tarballs
In this case, it makes sense not to hard-depend on svn.

So, if svn is missing, just say so, and add a comment in the
menuconfig.

Reported-by: ANDY KENNEDY <ANDY.KENNEDY@adtran.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Default test suite configuration

# Default DejaGnu configuration

DG_TOOLNAME = gcc

DG_TARGET_HOSTNAME = 127.0.0.1

DG_TARGET_USERNAME = root

# Default tests

DG_C_TESTS = 

DG_CPP_TESTS =