This tool is used for SPGO and is invoked directly by users as described
in the Clang User's Manual[^1].
This change will include llvm-profgen in installations configured with
LLVM_INSTALL_TOOLCHAIN_ONLY, such as those provided by LLVM's executable
Windows installers. This is useful now that LLVM can perform SPGO on
Windows.
[^1]:
https://clang.llvm.org/docs/UsersManual.html#using-sampling-profilers