scripts: in case of failed download, remove partial files

It happens from time to time that the server mis-behaves, and breaks the
connection right in the middle of nowhere, for no good reason, leaving us
with a partial file, on which the extract pass would choke.

Remove partial downloads, to fail early.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from eefacabd9e72f3d578e5dc5908026ed780f9a240)

--- gcc-4.0.0/libstdc++-v3/configure-old	2005-04-30 22:04:48.061603912 -0500

+++ gcc-4.0.0/libstdc++-v3/configure	2005-04-30 22:06:13.678588152 -0500

@@ -7194,6 +7194,9 @@

 cat >>conftest.$ac_ext <<_ACEOF

 /* end confdefs.h.  */

 #include <complex.h>

+#ifdef __UCLIBC__

+#error ugly hack to make sure configure test fails here for cross until uClibc supports the complex funcs

+#endif

 int

 main ()

 {