Another issue i faced today, now with /usr/ports/contrib/libvpx:

---
    [CC] test/../md5_utils.c.o
    [CC] test/../nestegg/halloc/src/halloc.c.o
In file included from test/../nestegg/halloc/src/halloc.c:19:0:
test/../nestegg/halloc/src/align.h:33:25: error: conflicting types for 'max_align_t'
 typedef union max_align max_align_t;
                         ^
In file included from test/../nestegg/halloc/src/../halloc.h:18:0,
                 from test/../nestegg/halloc/src/halloc.c:18:
/usr/lib/gcc/x86_64-unknown-linux-gnu/5.2.0/include/stddef.h:429:3: note: previous declaration of 'max_align_t' was here
 } max_align_t;
   ^
Makefile:128: recipe for target 'test/../nestegg/halloc/src/halloc.c.o' failed
make[1]: *** [test/../nestegg/halloc/src/halloc.c.o] Error 1
Makefile:17: recipe for target '.DEFAULT' failed
make: *** [.DEFAULT] Error 2
---