Use the static string in the presence of optimization.
Merge topic 'minor-cleanups' into next

c2baaa06 Use the static string in the presence of optimization.
Features: Use the features symbol in the feature-test compile.

Clang discards the entire string if it is not used, removing
the ability to read the features from the compiled binary. That
is prevented by using the symbol.

GNU with -O3 also discards the string, so use the string in a
way which is determined by a runtime value (argc) to prevent
it being discarded.
Merge topic 'minor-cleanups' into next

f6f10954 Features: Use the features symbol in the feature-test compile.