siggen: use correct umask when writing siginfo
We try to write sstate with group-write permissions so that sstate-cache
can be shared between multiple users. However the siginfo files are
created in various tasks which may set their own umask (such as
do_populate_sysroot, 0022). This results in no group write permission
on the intermediate directories, which is fatal when sharing a cache.
Fix this by wrapping the siginfo mkdir in a umask change to 0002.
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>