Because we don't now if a *.h file is a C or C++ header we provide both
as project file if a C and C++ file is present. But C++ is not readable
by C compiler. So we skip that files and hope there is no non referenced
C header, which is very very unlikely.

Change-Id: I5505713e759749c8a0738e11b70bb6b309412966
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>