Implement atan builtin

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@213759 91177308-0d34-0410-b5e6-96231b3b80d8
Implement atan2 builtin

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@213760 91177308-0d34-0410-b5e6-96231b3b80d8
Implement cos builtin for float types

The double version still uses @llvm.cos.

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@213761 91177308-0d34-0410-b5e6-96231b3b80d8
Implement sin builtin for float types

This double version still uses @llvm.sin.

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@213762 91177308-0d34-0410-b5e6-96231b3b80d8