common: reorder checking files' extension in check-headers.h

Reorder checking files' extension according to number
of each kind of files in order to make it (hopefully) faster.
Currently there are:
- 103 *.c files - check them as 1st,
-  38 *.h files - check them as 2nd and
-  31 *.sh and *.cmake files - check them as 3rd.