When trying to compile the Emacs Treesiter branch, I got the following
compilation error:

In file included from emacs.c:140:
./treesit.h:23:10: fatal error: 'tree_sitter/api.h' file not found
#include <tree_sitter/api.h>
         ^~~~~~~~~~~~~~~~~~~
1 error generated.

The reason is that the Makefile is not referring to the correct C
compiler flags because of a typo.  I've attached a patch to correct the
problem.

Thanks.