Merge pull request #2821 from jeromecoutant/PR_STM32F091RC

[STM32F091RC] patch for tests-mbedmicro-rtos-mbed-threads

Author: sg-

TESTS/mbedmicro-rtos-mbed/threads/main.cpp

@@ -17,7 +17,7 @@
  */
 #if defined(TARGET_MCU_NRF51822) || defined(TARGET_MCU_NRF52832)
     #define STACK_SIZE 512
-#elif (defined(TARGET_STM32F070RB) || defined(TARGET_STM32F072RB) || defined(TARGET_STM32F103RB))
+#elif defined(TARGET_STM32F070RB) || defined(TARGET_STM32F072RB) || defined(TARGET_STM32F103RB) || defined(TARGET_STM32F091RC)
     #define STACK_SIZE 512
 #else
     #define STACK_SIZE DEFAULT_STACK_SIZE