mbed_toolchain: Use C++11/C11 attributes

Newer language standards have standard forms for `MBED_NORETURN` and
`MBED_ALIGN` attributes. Use them when available.

C++14 also adds `[[deprecated]]`, but as it needs to go in the middle of
structure definitions as `class [[deprecated]] MyClass`, it's not a
total drop-in-replacemend for `MBED_DEPRECATED`, so that is not
attempted here.

Using standard forms increases the chances that code analysis tools such
Coverity will recognise them - particularly important for "no return".

platform/mbed_toolchain.h

@@ -72,7 +72,11 @@
  *  @endcode
  */
 #ifndef MBED_ALIGN
-#if defined(__ICCARM__)
+#if __cplusplus >= 201103 && !defined __CC_ARM
+#define MBED_ALIGN(N) alignas(N)
+#elif __STDC_VERSION__ >= 201112 && !defined __CC_ARM
+#define MBED_ALIGN(N) _Alignas(N)
+#elif defined(__ICCARM__)
 #define MBED_ALIGN(N) _Pragma(MBED_STRINGIFY(data_alignment=N))
 #else
 #define MBED_ALIGN(N) __attribute__((aligned(N)))
@@ -298,7 +302,11 @@
  *  @endcode
  */
 #ifndef MBED_NORETURN
-#if defined(__GNUC__) || defined(__clang__) || defined(__CC_ARM)
+#if __cplusplus >= 201103
+#define MBED_NORETURN [[noreturn]]
+#elif __STDC_VERSION__ >= 201112
+#define MBED_NORETURN _Noreturn
+#elif defined(__GNUC__) || defined(__clang__) || defined(__CC_ARM)
 #define MBED_NORETURN __attribute__((noreturn))
 #elif defined(__ICCARM__)
 #define MBED_NORETURN __noreturn