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>

Patch from upstream:

http://strace.cvs.sourceforge.net/viewvc/strace/strace/linux/arm/syscallent.h?r1=1.17&r2=1.18&sortby=file

2008-11-13  Kirill A. Shutemov  <kirill@shutemov.name>

    * linux/arm/syscallent.h: Fix build on ARM EABI which does not

    provide syscalls socketcall and ipc.

--- strace-4.5.18.orig/linux/arm/syscallent.h	2008/12/29 20:04:15	1.17

+++ strace-4.5.18/linux/arm/syscallent.h	2009/01/01 23:20:38	1.18

@@ -431,6 +431,7 @@

 	{ 5,	0,	printargs,		"SYS_398"	}, /* 398 */

 	{ 5,	0,	printargs,		"SYS_399"	}, /* 399 */

+#ifndef __ARM_EABI__

 #if SYS_socket_subcall != 400

  #error fix me

 #endif

@@ -481,3 +482,4 @@

 	{ 4,	TI,	sys_shmdt,		"shmdt"		}, /* 440 */

 	{ 4,	TI,	sys_shmget,		"shmget"	}, /* 441 */

 	{ 4,	TI,	sys_shmctl,		"shmctl"	}, /* 442 */

+#endif