The Clang gcc-compatible driver (clang/tools/driver/driver.cpp) has some logic to select an alternate target based on the executable it was called as. For instance, if you symlink i686-linux-android-gcc to clang and invoke it, the driver will act as though it were called with another argument ("-target i686-linux-android"). This leads to visible effects even in syntax-only compilations (like the ANDROID preprocessor symbol being defined).
This behavior is not replicated for tool invocations--for instance, clang::createInvocationFromCommandLine will not choose an alternate target based on ArgList. This means that configurations stored in compilation databases aren't accurately replayed.
This diff separates the logic for selecting a mode flag and target from the executable name into a new member function on ToolChain. It should have no functional effects (but will allow other code to reuse the target/mode selection logic).