Hey all, I think I may have a small fix for executing C source blocks in 
org-babel. Or, possibly just a bad case of user error.

The issue (in emacs 27 with -q) is that it doesn't seem possible to 
specify non-system header files with the :includes header argument.

For example; while the following line:

     #+BEGIN_SRC C :includes <example.h>

...produces reasonable code...

     #include <example.h>

...all of the following lines...

     #+BEGIN_SRC C :includes example.h

     #+BEGIN_SRC C :includes "example.h"

     #+BEGIN_SRC C :includes "\"example.h\""

...just result in this...

     #include example.h

...rather than this...

     #include "example.h"

The attached patch will wrap filenames in quotes if they do not begin 
with "<", and works for me.

Is this a reasonable fix, or maybe I'm misusing the feature?