IAR: try with attribute((__noreturn__)) first (#284)

Fixes #279 
Fixes #198

Author: RobinKastberg

CMSIS/Core/Include/cmsis_iccarm.h

@@ -55,7 +55,9 @@
 #endif
 
 #ifndef   __NO_RETURN
-  #if defined(__cplusplus) && __cplusplus >= 201103L
+  #if defined(__has_attribute) && __has_attribute(__noreturn__)
+    #define __NO_RETURN __attribute__((__noreturn__))
+  #elif defined(__cplusplus) && __cplusplus >= 201103L
     #define __NO_RETURN [[noreturn]]
   #elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
     #define __NO_RETURN _Noreturn

CMSIS/Documentation/Doxygen/Core/src/ref_compiler_ctrl.txt

@@ -169,7 +169,8 @@ __STATIC_FORCEINLINE uint32_t NVIC_GetVector(IRQn_Type IRQn)
 \brief Inform the compiler that a function does not return.
 \details
 Informs the compiler that the function does not return. The compiler can then perform optimizations by
-removing code that is never reached.
+removing code that is never reached. For maximum portability, this should only be used where the C/C++
+standard allows it.
 
 <b>Code Example:</b>
 \code

CMSIS/Documentation/Doxygen/Core_A/src/ref_compiler_ctrl.txt

@@ -107,7 +107,8 @@ __STATIC_FORCEINLINE uint32_t NVIC_GetVector(IRQn_Type IRQn)
 \brief Inform the compiler that a function does not return.
 \details
 Informs the compiler that the function does not return. The compiler can then perform optimizations by
-removing code that is never reached.
+removing code that is never reached. For maximum portability, this should only be used where the C/C++
+standard allows it.
 
 <b> Code Example:</b>
 \code