A toolchain Id is based on its canonical path.

e.g. For QtC 2.4 on Windows, the toolchain Id for the bundled mingw/gdb is:
ProjectExplorer.ToolChain.Mingw:C:/Qt/qtcreator-2.4.0/mingw/bin/gcc.exe.x86-windows-msys-pe-32bit.C:/Qt/qtcreator-2.4.0/pythongdb/gdb-i686-pc-mingw32.exe

On Windows, the default installation path changes for each version. That makes it hard to maintain custom toolchains.

We have a cross-debugger which we install in pythongdb. For each version of QtC we need to update not only the toolChains.xml file, but also the pro.shared file for the new path. This also doesn't work with multiple versions of QtC.