This makes the behavior similar to cp
```
chmod u+s,g+s,o+x a
sudo llvm-strip a -o b
// With this patch, b drops set-user-ID and set-group-ID bits.
// sudo cp a b => b does not have set-user-ID or set-group-ID bits.
```
This also changes the behavior for the following case:
```
chmod u+s,g+s,o+x a
llvm-strip a
// a preserves set-user-ID and set-group-ID bits.
// This matches binutils<2.36 and probably >=2.37. 2.36 and 2.36.1 have some compatibility issues.
```
Differential Revision: https://reviews.llvm.org/D97253
There is currently an EPERM error when a regular user executes `llvm-objcopy a.o /dev/null`.
Worse, root can even change the mode bits of /dev/null.
Fix it by checking if the output file is special.
A new overload of llvm::sys::fs::setPermissions with FD as the parameter
is added. Users should provide `perm & ~umask` as the parameter if they
intend to respect umask.
The existing overload of llvm::sys::fs::setPermissions may be deleted if
we can find an implementation of fchmod() on Windows. fchmod() is
usually better than chmod() because it saves syscalls and can avoid race
condition.
Reviewed By: jakehehrlich, jhenderson
Differential Revision: https://reviews.llvm.org/D64236
llvm-svn: 365753
Fangrui Song