add gcc flag -Wno-format-truncation to usrsctp when using b2

Jamfile

@@ -96,7 +96,7 @@ rule make_libusrsctp ( targets * : sources * : properties * )
 }
 actions make_libusrsctp
 {
-    (cd $(CWD)/deps/usrsctp && mkdir $(BUILD_DIR) && cd $(BUILD_DIR) && cmake -DCMAKE_BUILD_TYPE=$(VARIANT) -DCMAKE_C_FLAGS="-fPIC" .. && make -j2 usrsctp-static)
+    (cd $(CWD)/deps/usrsctp && mkdir $(BUILD_DIR) && cd $(BUILD_DIR) && cmake -DCMAKE_BUILD_TYPE=$(VARIANT) -DCMAKE_C_FLAGS="-fPIC -Wno-unknown-warning-option -Wno-format-truncation" .. && make -j2 usrsctp-static)
     cp $(CWD)/deps/usrsctp/$(BUILD_DIR)/usrsctplib/libusrsctp.a $(<)
 }
 rule make_libusrsctp_msvc ( targets * : sources * : properties * )