[waf] Add check for and link against libexecinfo on FreeBSD

src/main/wscript

@@ -16,6 +16,8 @@ def configure(conf):
 
 def build(bld):
 	libs = ['glib', 'gthread', 'gmodule', 'ev']
+	if sys.platform.startswith('freebsd'):
+		libs += ['execinfo']
 
 	source = '''
 		actions.c

wscript

@@ -154,8 +154,12 @@ def configure(conf):
 	conf.check(header_name='sys/resource.h')
 	conf.check(header_name='sys/sendfile.h')
 	conf.check(header_name='sys/un.h')
-	conf.check(header_name='execinfo.h')
-	
+
+	if sys.platform.startswith('freebsd'):
+		conf.check(lib='execinfo', uselib_store='execinfo', define_name="HAVE_EXECINFO_H")
+	else:
+		conf.check(header_name='execinfo.h', define_name="HAVE_EXECINFO_H")
+
 	# check for available functions
 	if sys.platform == 'linux2':
 		conf.check(function_name='sendfile', header_name='sys/sendfile.h', define_name='HAVE_SENDFILE')