Revert "[llvm] Disable HandleLLVMOptions in runtimes mode (#73031)"

This appears to have caused a variety of breakages, see comments on the PR.

> Summary:
> There are a few default options that LLVM adds that can be problematic
> for runtimes builds. These options are generally intended to handle
> building LLVM itself, but are also added when building in a runtimes
> mode. One such issue I've run into is that in `libc` we deliberately use
> `--target` to use a different device toolchain, which doesn't support
> some linker arguments passed via `-Wl`. This is observed in
> https://github.com/llvm/llvm-project/pull/73030 when attempting to use
> these options.
>
> This patch completely removes these default arguments.
>
> The consensus is that any issues created by this patch should ultimately
> be solved on a per-runtime basis.

This reverts commit ee922e6ebf.

runtimes/CMakeLists.txt

@@ -151,7 +151,9 @@ endif()
 # Avoid checking whether the compiler is working.
 set(LLVM_COMPILER_CHECKED ON)
 
+# Handle common options used by all runtimes.
 include(AddLLVM)
+include(HandleLLVMOptions)
 
 find_package(Python3 REQUIRED COMPONENTS Interpreter)