Add llvm::apply to STLExtras.

This is equivalent to the C++14 std::apply().  Since we are not
using C++14 yet, this allows us to still make use of apply anyway.

Differential revision: https://reviews.llvm.org/D25100

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@283779 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed