[LLVM-C] Audit Inline Assembly APIs for Consistency

Summary:
- Add a missing getter for module-level inline assembly
- Add a missing append function for module-level inline assembly
- Deprecate LLVMSetModuleInlineAsm and replace it with LLVMSetModuleInlineAsm2 which takes an explicit length parameter
- Deprecate LLVMConstInlineAsm and replace it with LLVMGetInlineAsm, a function that allows passing a dialect and is not mis-classified as a constant operation

Reviewers: whitequark, deadalnix

Reviewed By: whitequark

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D45346

llvm-svn: 329369