wasi-sdk-7

Changes to wasi-libc 8df0d4c..c9a5733:

Set the MALLOC_ALIGNMENT to 16.
When checking undefined symbol list, ignore certain llvm buildins
Fix a warning about a spurious redundant static keyword.
Update docs to say "libc" rather than "sysroot" where applicable.
WASI libc's dirent does have t_type, so define _DIRENT_HAVE_D_TYPE.
Fix DIRENT_HAVE_D* macros.
Disable the lseek optimization in C++.
Add Azure Pipelines definition (#78)
Update to musl 1.1.23.

Changes to llvm:

use release tag llvmorg-9.0.0

Changes to wasi-sdk:

Documentation updates