This allows the wrappers to invoke the right tool with the right
options, even when the wrapper was invoked with an obfuscated
short form file name.
This happens e.g. when CMake/Ninja invokes the tools from a path
that contains spaces.
Normally, we'd split the string at the last dash. However if the
tool name is "llvm-<tool>", make sure to include "llvm-" in the
tool name part when splitting the executable name.
In llvm-wrapper, don't add a duplicate "llvm-" prefix for the tool
name in these cases.
This saves a lot of diskspace, when symlinks are turned into full
copies of the tools on windows, as the symlinks only point to a small
wrapper instead of to the full tool.
Martin Storsjö