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, 8 insertions, 0 deletions

diff --git a/Help/release/dev/delay-generator-toolset.rst b/Help/release/dev/delay-generator-toolset.rst
new file mode 100644
index 0000000..0512834
--- /dev/null
+++ b/Help/release/dev/delay-generator-toolset.rst
@@ -0,0 +1,8 @@
+delay-generator-toolset
+-----------------------
+
+* The :variable:`CMAKE_GENERATOR_TOOLSET` variable may now be
+  initialized in a toolchain file specified by the
+  :variable:`CMAKE_TOOLCHAIN_FILE` variable.  This is useful
+  when cross-compiling with the Xcode or Visual Studio
+  generators.