[foreign] RFR 8213013: jextract does not handle C99 _Complex type

[Sundararajan Athijegannathan]

Please review support for C99 _Complex type. Note that "long double" is 
not yet supported by the binder (a separate bug has been filed). So 
"long double _Complex" won't work yet. I tested this patch on Mac and 
Linux. Because of the way complex.h declares functions (using a macro 
from <bits/cmathcalls.h>), jextract does not extract anything useful 
with complex.h. I had to redeclare functions of interest in mycomplex.h. 
In any case, long double _Complex handling functions won't work on Mac 
as well - hence mycomplex.h file.

Bug: https://bugs.openjdk.java.net/browse/JDK-8213013
Webrev: https://cr.openjdk.java.net/~sundar/8213013/webrev.00/index.html

Thanks,
-Sundar