Add llvm-pdbutil in LLVM_TOOLCHAIN_TOOLS

[hans]

Summary

One can argue that it qualifies as a toolchain tool rather than "internal llvm
tool". This will make it part of builds which set the
LLVM_INSTALL_TOOLCHAIN_ONLY cmake option, such as the Windows installer.

[aganea]

Thanks @hans!

llvm/cmake/modules/AddLLVM.cmake

set (LLVM_TOOLCHAIN_TOOLS
     llvm-cxxfilt
     llvm-dwp
     llvm-ranlib
     llvm-lib
     llvm-ml
     llvm-nm
     llvm-objcopy
     llvm-objdump
+    llvm-pdbutil
     llvm-rc
     llvm-readobj
     llvm-size
     llvm-strings
     llvm-strip
     llvm-profdata
     llvm-symbolizer
     # symlink version of some of above tools that are enabled by