Expect tests to specify stderr content if it is present.
Fix the CMP0019 test, which has only been testing the WARN status
until now. Specify in the CommandLine and FPHSA tests that content
is at least one character.
Set policies in the Language and CheckModules tests, which have empty
test output, modulo unrelated policies on some platforms.
Enable the C and CXX languages only in the test cases that really need
them. In the failure cases we do not get far enough to really use the
languages, so skip enabling them.
Previously if headers required to check if a struct has a member can be
compiled with C++ compiler only, the check would fail because the C
compiler fails. As a consequence, the result variable would be set to
false, even if the struct has that particular member.
Teach CHECK_STRUCT_HAS_MEMBER to accept a new optional argument LANGUAGE
that allows one to explicitly set the compiler to use. The new
signature is therefore:
CHECK_STRUCT_HAS_MEMBER (<struct> <member> <header> <variable>
[LANGUAGE <language>])
