Commit 089f627 leads to library linking errors due to header file missing <stdbool.h>

[sbates130272]

In 089f627 we added bounds_checks and introduced the bool type in ubpf.h which requires that <stdbool.h> be added to the include path. Since <stdbool.h> was already used internally this did not impact the compilation of libubpf.a. However this does cause a regression issue when linking to the library from a program that does currently include <stdbool.h>.

For example prior to commit 089f627 the following would compile using gcc:

#include <ubpf.h>                                                                                                                                                                                                                                                               
int main(void) { ubpf_create(); return 0; }

but post this commit this now fails with

/usr/local/include/ubpf.h:36:1: error: unknown type name 'bool'
   36 | bool toggle_bounds_check(struct ubpf_vm *vm, bool enable);
      | ^~~~
/usr/local/include/ubpf.h:36:46: error: unknown type name 'bool'
   36 | bool toggle_bounds_check(struct ubpf_vm *vm, bool enable);
      |                                              ^~~~

I think the correct way to solve this is to add <stdbool.h> to the external facing header file (ubpf.h) and optionally remove this from the internal files. I am happy to do a patch for this if required.