Fix UAVCAN bootloader builds broken by os calls from stm32_flash

Recent upsteam NuttX changes needed by PX4 added sem_[wait|post]
   in the stm32_flash driver.

   UAVCAN Bootloaders do not use the OS's scheduler etal.
   This commit nops the sem_[wait|post] with linker magic.
   Which precludes the linking the nuttx scheduler in the
   bootloader build.

src/drivers/bootloaders/src/common/nuttx_stubs.c

@@ -0,0 +1,89 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2017 PX4 Development Team. All rights reserved.
+ *       Author: David Sidrane <david_s5@nscdg.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Types
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Function Prototypes
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Data
+ ****************************************************************************/
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+__EXPORT int __wrap_sem_wait(void *sem);
+__EXPORT int __wrap_sem_post(void *sem);
+
+/****************************************************************************
+ * Name: sem_wait and sem_post
+ *
+ * Description:
+ *   These functions hijacks by the way of a compile time wrapper the systems
+ *   sem_wait and sem_post functions.
+ *
+ ****************************************************************************/
+
+int __wrap_sem_wait(void *sem)
+{
+	return 0;
+}
+
+int __wrap_sem_post(void *sem)
+{
+	return 0;
+}

src/firmware/nuttx/CMakeLists.txt

@@ -29,7 +29,7 @@ set(startup_libs)
 if("${config_nuttx_config}" STREQUAL "bootloader")
 	set(nuttx_ld_prefix "bootloader")
 	set(nuttx_startup_files ${nuttx_export_dir}/startup/${nuttx_startup_files})
-	set(nuttx_bootloader_wrapers "-Wl,-wrap,sched_process_timer")
+	set(nuttx_bootloader_wrapers "-Wl,-wrap,sched_process_timer -Wl,-wrap,sem_post -Wl,-wrap,sem_wait")
 
 	add_custom_command(OUTPUT
 		${nuttx_startup_files}