Add a patch to fix cryptographic digest in command specification for shell
scripts and other interpreted files. Error happens because fexecve() requires
/dev/fd to be mounted. This patch detects if /dev/fd/N exists before attempt
to use fexecve and workaround the issue.

PR: 223587
Submitted by: Todd C. Miller <Todd.Miller@sudo.ws>
Reported by: vas@mpeks.tomsk.su
Obtained from: https://www.sudo.ws/repos/sudo/rev/30f7c5d64104
MFH: 2018Q2
Sponsored by: Rubicon Communications, LLC (Netgate)