Introduce mechanism to check standard conformance of headers

Introduce mechanism to check standard conformance of headers

While pretty simplistic, it appears to serve the purpose at the moment
(i.e. it spotted two places where a GNU extension was used withou
proper preprocessor conditionals). The "simplistic" here includes that
the checking gets only done for native builds, and ia64 gets excluded
due to its arch-specific header intentionally (for whatever reason)
checking that anonymous struct/unions can be used.

Signed-off-by: Jan Beulich <jbeulich@novell.com>