audio/bsequencer-lv2: fix build with GCC architectures

C++11 compiler is required:
cc1plus: error: unrecognized command line option "-std=c++11"

include sys/types.h is required by GCC for uint in src/BWidgets/ChoiceBox.cpp, src/BWidgets/ImageIcon.cpp and src/BWidgets/ListBox.cpp.

PR: 239440
Approved by: linimon (mentor), yuri (maintainer)
Differential Revision: https://reviews.freebsd.org/D21066