scripts/functions: svn retrieval first tries the mirror for tarballs

The svn download helper looks for the local tarballs dir to see if it
can find a pre-downloaded tarball, and if it does not find it, does
the actual fetch to upstream via svn.

In the process, it does not even try to get a tarball from the local
mirror, which can be useful if the mirror has been pre-populated
manually (or with a previously downloaded tree).

Fake a tarball get with the standard tarball-download helper, but
without specifying any upstream URL, which makes the helper directly
try the LAN mirror.

Of course, if no mirror is specified, no URL wil be available, and
the standard svn retrieval will kick in.

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

# GMP options

choice

    bool

    prompt "GMP version"

# Don't remove next line

# CT_INSERT_VERSION_BELOW

config GMP_V_5_0_1

    bool

    prompt "5.0.1 (EXPERIMENTAL)"

    depends on EXPERIMENTAL

config GMP_V_4_3_2

    bool

    prompt "4.3.2"

config GMP_V_4_3_1

    bool

    prompt "4.3.1"

config GMP_V_4_3_0

    bool

    prompt "4.3.0"

config GMP_V_4_2_4

    bool

    prompt "4.2.4 (OBSOLETE)"

    depends on OBSOLETE

config GMP_V_4_2_2

    bool

    prompt "4.2.2 (OBSOLETE)"

    depends on OBSOLETE

endchoice

config GMP_VERSION

    string

# Don't remove next line

# CT_INSERT_VERSION_STRING_BELOW

    default "5.0.1" if GMP_V_5_0_1

    default "4.3.2" if GMP_V_4_3_2

    default "4.3.1" if GMP_V_4_3_1

    default "4.3.0" if GMP_V_4_3_0

    default "4.2.4" if GMP_V_4_2_4

    default "4.2.2" if GMP_V_4_2_2