Simply compiling a C header with a C++ compiler is not enough to flag
missing 'extern "C"' guards. To catch missing guards, we can just use a
simple grep for the 'extern "C"' part, and error out if any files have a
miss.
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>