waf: allow to disable lttng at configuration

We default to autodetection for LTTNG so if the libraries are available
we enable it. However this may not always be desired.

Tools/ardupilotwaf/cxx_checks.py

@@ -151,6 +151,10 @@ def check_librt(cfg, env):
 
 @conf
 def check_lttng(cfg, env):
+    if cfg.options.disable_lttng:
+        cfg.msg("Checking for 'lttng-ust':", 'disabled', color='YELLOW')
+        return False
+
     cfg.check_cfg(package='lttng-ust', mandatory=False, global_define=True,
                   args=['--libs', '--cflags'])
     env.LIB += cfg.env['LIB_LTTNG-UST']

wscript

@@ -82,6 +82,10 @@ revisions.
         default=False,
         help='Configure as debug variant.')
 
+    g.add_option('--disable-lttng', action='store_true',
+        default=False,
+        help="Don't use lttng even if supported by board and dependencies available")
+
 def _collect_autoconfig_files(cfg):
     for m in sys.modules.values():
         paths = []