cmTarget: Add CXX_STANDARD_REQUIRED to control decay.
Revert topic
Merge topic 'compile-features-C-language' into next

efd0c06d Revert topic
Merge topic 'decay-language-version' into next

38ce9519 cmTarget: Add CXX_STANDARD_REQUIRED to control decay.
Features: Record for GNU 4.7.

Update the CompileFeatures test to verify that unsupported features
do not work.
Merge topic 'GNU-4.7-features' into next

d6cc1e55 Features: Record for GNU 4.7.
Tests: Fix name of cache variable.
Help: Fix order of help entries.
Project: Remove extern from static string in feature tests.
Project: Use nullary form of main for compile feature tests.
Project: Fix exit-on-error with compile feature tests.
Features: Extend concept to C language.

Add properties and variables corresponding to CXX equivalents.

Add features for c_function_prototypes (C90), c_restrict (C99),
c_variadic_macros (C99) and c_static_assert (C11). This can be
extended later.
Merge topic 'compile-features-C-language' into next

ba5f12c1 Features: Extend concept to C language.
fe21aaae Project: Fix exit-on-error with compile feature tests.
5028fdc8 Project: Use nullary form of main for compile feature tests.
88f7b737 Project: Remove extern from static string in feature tests.
3521e0d9 Help: Fix order of help entries.
bdd33a1b Tests: Fix name of cache variable.