Add llvm-ml to LLVM_TOOLCHAIN_TOOLS (PR50536)

so that it gets installed in LLVM_INSTALL_TOOLCHAIN_ONLY builds,
such as used by the Windows installer.

Differential revision: https://reviews.llvm.org/D109358

llvm/cmake/modules/AddLLVM.cmake

@@ -1204,6 +1204,7 @@ if(NOT LLVM_TOOLCHAIN_TOOLS)
     llvm-cxxfilt
     llvm-ranlib
     llvm-lib
+    llvm-ml
     llvm-nm
     llvm-objcopy
     llvm-objdump