Bring the contrib/llvm/patches directory up-to-date.

MFC r263892:
Add the llvm/clang patch for r263891.

MFC r264350:
Update the llvm/clang patch for r264345.

MFC r266675:
Add the clang patch for r266674.

MFC r275651:
Add llvm patch corresponding to r275633.

MFC r275747:
Update llvm patches for r274286 and r275633 so all the tests will pass.

MFC r275760:
Add clang patch corresponding to r275759.

MFC r275772:
Update clang patch for r275759 to use correct test cases.

Additionally:

• Remove the clang patch corresponding to r263619, as ARM EABI hard-float support was never MFC'd.
• Add clang patch corresponding to r279302.