Fix ARM syscall argument loading.

Fix ARM syscall argument loading.

This patch is a uClibc equivalent of
<http://sourceware.org/ml/libc-ports/2008-11/msg00006.html>, to
compute all syscall arguments on ARM in temporary variables before
loading them into register variables.  The principle is as for that
glibc patch; the problem I actually observed was a GCC internal
compiler error building ld.so for Thumb-2.

Signed-off-by: Joseph Myers <joseph@codesourcery.com>