Rollup merge of #64317 - nikic:bump-llvm-3, r=alexcrichton
Rollup merge of #64317 - nikic:bump-llvm-3, r=alexcrichton

Update LLVM submodule

Updates the LLVM submodule to current LLVM 9 HEAD.

Fixes #63918.
Fixes #63791.

r? @alexcrichton

aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust