Prior to this patch, the `add_tablegen()` macro in
llvm/cmake/modules/TableGen.cmake added the install rule only if
`project` matched `LLVM` or `MLIR`. This patch adds an optional
`DESTINATION` argument, which, if non-empty, decides whether (and where)
to install the tablegen tool, thus eliminating the need for
project-specific overrides. This patch also updates all other
invocations of the `add_tablegen()` macro.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D131282
d1bb3016dd