Summary:
When used, it is substituted with the number of .macro instantiations we've done up to that point in time.
So if this is the 1st time we've instantiated a .macro (any .macro, regardless of name), \@ will instantiate to 0, if it's the 2nd .macro instantiation, it will instantiate to 1 etc.
It can only be used inside a .macro definition, an .irp definition or an .irpc definition (those last 2 uses are undocumented).
Reviewers: echristo, rafael
Reviewed By: rafael
Subscribers: dsanders, llvm-commits
Differential Revision: http://reviews.llvm.org/D9197
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235862 91177308-0d34-0410-b5e6-96231b3b80d8
