Improve reproducibility of XBPS packages

XBPS packages don't seem to have an option to manipulate file
permissions at package creation time.

So as a best effort, set the umask as soon as possible to ensure
file permissions are the same when running the bootstrap.

This is enough to allow reproducible XBPS packages when starting the
bootstrap with a umask different than 0022.

sysc/run2.sh

@@ -17,6 +17,8 @@ trap 'env - PATH=${PREFIX}/bin PS1="\w # " bash -i' EXIT
 
 trap bash EXIT
 
+umask 0022
+
 build xz-5.0.5
 
 build automake-1.11.2