Namespace with language.
Merge topic 'WriteCompilerDetectionHeader-module' into next

0ac001e8 Namespace with language.
Add the WriteCompilerDetectionHeader module.

Provide a function to write a portable header to detect compiler
features.  Generate a preprocessor #error for unknown compilers
and compiler versions whose features are not yet recorded.  This
error condition might be relaxed in the future, but for now it
is useful for verification of expectations.
Merge topic 'WriteCompilerDetectionHeader-module' into next

2c1823ea Add the WriteCompilerDetectionHeader module.