LLVM has a known leak, which is addressed by this patch:
https://reviews.llvm.org/. With this patch, and making sure that
llvm::shutdown() is called, AppVerifier on Windows, and LSAN on Linux,
report no more load/unload leaks.

Bug: b/175782868
Bug: chromium:972686
Bug: angleproject:5377
Change-Id: If34a00c3a4b845604445f22bdb5889f51bb5a1d6
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/52168
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>