Improve error-prone condition handling

[mrexodia]

[project]
name = "MYPROJECT"

[options]
MYPROJECT_TESTS = "root"

[target.tests]
condition = "MYPROJECT_TESTS"

This would generate a # NOTE: unnamed condition even though MYPROJECT_TESTS is an option defined in the project. Additionally making a typo like MYPROJECT_TSETS would silently emit if(MYPROJECT_TSETS) # NOTE: unnamed condition instead of raising an error.

This issue was introduced because raw conditions are now supported, for instance:

[target.foo]
sources = ["foo.cpp"]
"WIN32 OR APPLE".sources = ["bar.cpp"]