fix Makefile.am in src dir

[ghost]

1. I am not sure if this is a fix, I am on Crux Linux, this is a fix for me. (Thanks to @condy0919 )
2. Also you guys said installing libffi-devel can fix, I am curious about how that did the trick.
3. it's a great project, thanks,

@taviso Can you amswer my question and review this PR? Thanks for your time.

[ghost]

Also Crux Linux, no devel pkg such thing. so i am really curious :)

[cemeyer]

I would guess that on most Linux distributions, installing the devel package installs the headers directly in /usr/include, which is the global include path. If the headers don't get installed in global /usr/include (e.g. Crux's libffi does this: https://crux.nu/ports/crux-3.2/opt/libffi/.footprint ), then we need $(FFI_CFLAGS) as the patch suggests.

(Fedora just drops them directly in /usr/include:)

$ rpm -ql libffi-devel
/usr/include/ffi-x86_64.h
/usr/include/ffi.h
/usr/include/ffitarget-x86_64.h
/usr/include/ffitarget.h
...

Anyway, the suggested fix seems fine to me.

[taviso]

I thought the libstruct code didn't use any libffi stuff...but it seems like a harmless patch, so I think it's okay if this fixes it for you.

I can merge.

[taviso]

Done, thanks @rtlanceroad!

[cemeyer]

struct.c includes ffi.h. :-)

[ghost]

Thanks for the explaination for devel pkg @cemeyer :) And also merging this PR @taviso :)

[ghost]

I only see in struct.c, there are less than 10 lines related to ffi.h, maybe in the furture we want to drop libffi support?

[cemeyer]

Why bother? We use ffi widely in the rest of ctypes.sh, so you would still need it installed to compile and use ctypes.sh.

[ghost]

ok ;)