All libcalls should be considered to be GC-leaf functions.

All libcalls should be considered to be GC-leaf functions.

Summary:
It is possible for some passes to materialize a call to a libcall (ex: ldexp, exp2, etc),
but these passes will not mark the call as a gc-leaf-function. All libcalls are
actually gc-leaf-functions, so we change llvm::callsGCLeafFunction() to tell us that
available libcalls are equivalent to gc-leaf-function calls.

Reviewers: sanjoy, anna, reames

Reviewed By: anna

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D35840

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309291 91177308-0d34-0410-b5e6-96231b3b80d8