rust: Enable dynamic linking with llvm

rust: Enable dynamic linking with llvm

Fixes [Yocto #16058]

A segmentation fault occurs in rustc (e.g. in
llvm::X86ReadAdvanceTable) when reusing sstate artifacts built with
different host toolchain versions.

Issue sequence:
1. llvm-native is built with a newer toolchain
   (e.g. GCC 15/Binutils 2.45).
2. rust-native is later built with an older linker.
   (e.g. GCC 12/Binutils 2.40).
3. The older linker statically links parts of llvm-native into
   librustc_driver.
4. The resulting binary crashes at runtime inside the statically
   linked LLVM code.

The corruption happens at link time when mixing static native objects
produced by different toolchain generations.

Enable dynamic LLVM linking (link-shared = true) for rust-native so rustc
links against libLLVM.so instead of static archives, avoiding host linker
incompatibilities when reusing sstate artifacts.

Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
Suggested-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>