On Alpha, the register $at is, by default, reserved for use by the
assembler, in the expansion of pseudo-instructions. It's also used
by the special calling convention for _mcount. We get warnings from
Alpha clone.S because the code to call _mcount isn't properly marked
up to tell the assembler not to use $at itself.
* sysdeps/unix/sysv/linux/alpha/clone.s (__clone): Wrap manual
uses of $at in .set noat / .set at.
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