Ensure that const and pure function attributes are used properly (#1739)

Some functions were incorrectly marked as const but were pure only
(or not even pure). Some functions were marked as pure but
qualified as const. Some functions were not attributed at all but
qualified either as pure or const. Some functions had attributes
at definition but not at declaration. This commit fixes these
inconsistencies.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

jerry-core/jmem/jmem.h

@@ -16,6 +16,8 @@
 #ifndef JMEM_H
 #define JMEM_H
 
+#include "jrt.h"
+
 /** \addtogroup mem Memory allocation
  * @{
  *
@@ -143,8 +145,8 @@ void jmem_stats_reset_peak (void);
 void jmem_stats_print (void);
 #endif /* JMEM_STATS */
 
-jmem_cpointer_t jmem_compress_pointer (const void *pointer_p);
-void *jmem_decompress_pointer (uintptr_t compressed_pointer);
+jmem_cpointer_t jmem_compress_pointer (const void *pointer_p) __attr_pure___;
+void *jmem_decompress_pointer (uintptr_t compressed_pointer) __attr_pure___;
 
 /**
  * A free memory callback routine type.