waf: add libiio support for bebop

check for the presence of libiio to enable the compilation of
the bebop rangefinder that needs it.
If the build remains static, there needs to be a rootfs that contains
the libiio.a file because it is not included in the debian package.
A solution can be to compile libiio and copy libiio.a in /usr/lib[/arch]

Tools/ardupilotwaf/boards.py

@@ -277,6 +277,11 @@ class bebop(linux):
     def configure_env(self, cfg, env):
         super(bebop, self).configure_env(cfg, env)
 
+        cfg.check_cfg(package='libiio', mandatory=False, global_define=True,
+                args = ['--libs', '--cflags'])
+
+        env.LIB += cfg.env.LIB_LIBIIO
+
         env.DEFINES.update(
             CONFIG_HAL_BOARD_SUBTYPE = 'HAL_BOARD_SUBTYPE_LINUX_BEBOP',
         )

Tools/ardupilotwaf/toolchain.py

@@ -125,6 +125,7 @@ def configure(cfg):
     _filter_supported_cxx_compilers('g++', 'clang++')
 
     cfg.env.AR = cfg.env.TOOLCHAIN + '-ar'
+    cfg.env.PKGCONFIG = cfg.env.TOOLCHAIN + '-pkg-config'
     cfg.msg('Using toolchain', cfg.env.TOOLCHAIN)
     cfg.load('compiler_cxx compiler_c')