package/llvm: specify LLVM_ENABLE_BINDINGS=OFF

package/llvm: specify LLVM_ENABLE_BINDINGS=OFF

LLVM builds bindings for other languages such as Go and OCaml when the
appropriate dependencies can be found. We currently don't support
building these bindings in Buildroot, as they're currently unused by any
package.

Building these bindings was originally disabled by overriding the
dependencies with values indicating that they were not found.

Newer versions of LLVM no longer disable the OCaml bindings when overriding
OCAMLFIND. Consequently, the build process attempts to install the bindings
to the default location on the host of /usr/lib/ocaml/llvm, causing a
permissions error and build failure.

Additionally, LLVM has since added the variable LLVM_ENABLE_BINDINGS to
control whether bindings are enabled, so we override that to disable the
bindings.

Signed-off-by: Joseph Kogut <joseph.kogut@gmail.com>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>