meson: Make shared-llvm into a tri-state boolean
Choosing LLVM's link mode is legitimate on UNIX systems, but only static actually really works under Windows.
Give shared-llvm a default 'auto' mode which will pick the previous default of true (shared) on UNIX systems, but newly defaulting to false (static) on Windows.
Signed-off-by: Daniel Stone daniels@collabora.com Suggested-by: Dylan Baker dylan@pnwbakers.com
/cc @dbaker @jrfonseca