[LLVM-C] Improve Intrinsics Bindings

Summary:
Improve the intrinsic bindings with operations for

- Retrieving and automatically inserting the declaration of an intrinsic by ID
- Retrieving the name of a non-overloaded intrinsic by ID
- Retrieving the name of an overloaded intrinsic by ID and overloaded parameter types

Improve the echo test to copy non-overloaded intrinsics by ID.

Reviewers: whitequark, deadalnix

Reviewed By: whitequark

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D53626

llvm-svn: 346195