Improve code quality for alloc_size (#196)

* Improve code quality for alloc_size

* Made error noreturn.

* Update docs.

* Move annoation

src/pal/pal.h

@@ -49,7 +49,7 @@ namespace snmalloc
     DefaultPal;
 #endif
 
-  SNMALLOC_SLOW_PATH inline void error(const char* const str)
+  [[noreturn]] SNMALLOC_SLOW_PATH inline void error(const char* const str)
   {
     Pal::error(str);
   }

src/pal/pal_freebsd_kernel.h

@@ -29,7 +29,7 @@ namespace snmalloc
      * PAL supports.
      */
     static constexpr uint64_t pal_features = AlignedAllocation;
-    void error(const char* const str)
+    [[noreturn]] void error(const char* const str)
     {
       panic("snmalloc error: %s", str);
     }

src/pal/pal_open_enclave.h

@@ -5,7 +5,7 @@
 extern "C" const void* __oe_get_heap_base();
 extern "C" const void* __oe_get_heap_end();
 extern "C" void* oe_memset_s(void* p, size_t p_size, int c, size_t size);
-extern "C" void oe_abort();
+extern "C" [[noreturn]] void oe_abort();
 
 namespace snmalloc
 {
@@ -19,7 +19,7 @@ namespace snmalloc
      * PAL supports.
      */
     static constexpr uint64_t pal_features = 0;
-    static void error(const char* const str)
+    [[noreturn]] static void error(const char* const str)
     {
       UNUSED(str);
       oe_abort();

src/pal/pal_posix.h

@@ -55,7 +55,7 @@ namespace snmalloc
     /**
      * Report a fatal error an exit.
      */
-    static void error(const char* const str) noexcept
+    [[noreturn]] static void error(const char* const str) noexcept
     {
       puts(str);
       print_stack_trace();

src/pal/pal_windows.h

@@ -105,7 +105,7 @@ namespace snmalloc
       low_memory_callbacks.register_notification(callback);
     }
 
-    static void error(const char* const str)
+    [[noreturn]] static void error(const char* const str)
     {
       puts(str);
       fflush(stdout);