The try_compile command builds the cmTryCompileExec executable using the
cmTryCompileExec/fast target with Makefile generators in order to save
time since dependencies are not needed. However, in project mode the
command builds an entire source tree that may have dependencies.
Therefore we can use the /fast target approach only in one-source mode.
When building an entire source tree with try_compile instead of just a
single source file, it is possible that the CMakeLists.txt file in the
try-compiled project invokes try_compile. This commit fixes propagation
of language-initialization results from the outer-most project into any
number of try-compile levels.
The try_compile command project mode builds an entire source tree
instead of one source file. It uses an existing CMakeLists.txt file in
the given source tree instead of generating one. This commit creates a
test for the mode in the TryCompile test.
