This has led to a problem in my project where I linked objects compiled with gcc and clang and it took some time to find out why.
Will it be worth syncing the behavior with gcc?
On some targets, -fshort-enums is the default; this is determined by the ABI.
If this is so, clang must enforce it, too?
For each target clang supports, there are a bunch of target-specific configuration bits. Whether -fshort-enums is on by default is one of those. The only way for us to know if the default is wrong for some particular target triple is if someone files a bug report.
Are you concerned about some specific target?