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>

# dmalloc debug facility

## depends on ! BACKEND

##

## help dmalloc helps tracking memory allocation mis-usage

## help such as double-free, use-after-free...

choice

    bool

    prompt "dmalloc version"

# Don't remove next line

# CT_INSERT_VERSION_BELOW

config DMALLOC_V_5_5_2

    bool

    prompt "5.5.2"

endchoice

config DMALLOC_VERSION

    string

# Don't remove next line

# CT_INSERT_VERSION_STRING_BELOW

    default "5.5.2" if DMALLOC_V_5_5_2