The ctest_configure command already reads the CTEST_CMAKE_GENERATOR
variable to get the value for the cmake -G option. Read new variable
CTEST_CMAKE_GENERATOR_TOOLSET for -T.
The "ctest --build-and-test" mode already has "--build-generator" to
specify the -G option to CMake. Add a "--build-generator-toolset" option
to specify the -T value.
