Doxygenified some comments in IRBuilder.h.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173986 91177308-0d34-0410-b5e6-96231b3b80d8
Restrict sin/cos optimization to 64-bit only for now. 32-bit is a bit messy and less critical.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173987 91177308-0d34-0410-b5e6-96231b3b80d8
Forgot the test case before.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173988 91177308-0d34-0410-b5e6-96231b3b80d8