Allow a toolchain file to specify a generator toolset

Delay use of CMAKE_GENERATOR_TOOLSET until the CMakeSystem.cmake
file has been configured and loaded during the first project() or
enable_language() command.  This gives the toolchain file named by
CMAKE_TOOLCHAIN_FILE a chance to set CMAKE_GENERATOR_TOOLSET.  This
point is still early enough to set the generator toolset prior to
the initialization of any languages that might use the toolset.

The cmake::GeneratorToolset member variable remains an indication
of what was specified by the -T option or loaded from the cache.
It does not need to be updated based on the toolchain file setting.
The cmMakefile::TryCompile can still pass cmake::GeneratorToolset
into the inner instance because the try-compiled project will do
platform and language initialization using the CMakeSystem module
configured for the outer project.

Extend the RunCMake.GeneratorToolset test with cases that use a
toolchain file to set CMAKE_GENERATOR_TOOLSET.

1 files changed, 1 insertions, 1 deletions

diff --git a/Tests/RunCMake/GeneratorToolset/BadToolset-stderr.txt b/Tests/RunCMake/GeneratorToolset/BadToolset-stderr.txt
index bf1f190..d0d526c 100644
--- a/Tests/RunCMake/GeneratorToolset/BadToolset-stderr.txt
+++ b/Tests/RunCMake/GeneratorToolset/BadToolset-stderr.txt
@@ -1,4 +1,4 @@
-CMake Error:
+CMake Error at CMakeLists.txt:[0-9]+ \(project\):
   Generator
 
     .*