www/libxul: unbreak on 12.0 after r320240

cc -o Unified_c_media_libnestegg_src0.o -c ... -std=gnu99 ... Unified_c_media_libnestegg_src0.c
In file included from obj-i386-unknown-freebsd12.0/media/libnestegg/src/Unified_c_media_libnestegg_src0.c:2:
In file included from media/libnestegg/src/halloc.c:19:
media/libnestegg/src/align.h:42:25: error: typedef redefinition with different types ('union max_align' vs '__max_align_t')
typedef union max_align max_align_t;

^

/usr/include/stddef.h:67:23: note: previous definition is here
typedef __max_align_t max_align_t;

^

1 error generated.

Reported by: pkg-fallout