Fix compile warnings about always_inline functions in GCC 5.2.0

The warning is "always_inline function might not be inlinable", fixed by
adding inline keyword. See:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55830

JerryScript-DCO-1.0-Signed-off-by: Geoff Gustafson geoff@linux.intel.com

jerry-core/mem/mem-heap.c

@@ -115,7 +115,7 @@ typedef struct
 /**
  * Get end of region
  */
-static mem_heap_free_t *  __attr_always_inline___ __attr_pure___
+static inline mem_heap_free_t *  __attr_always_inline___ __attr_pure___
 mem_heap_get_region_end (mem_heap_free_t *curr_p) /**< current region */
 {
   return (mem_heap_free_t *)((uint8_t *) curr_p + curr_p->size);
@@ -413,7 +413,7 @@ mem_heap_alloc_block (const size_t size)
  *
  * Note: block will only be aligned to 4 bytes.
  */
-void * __attr_always_inline___
+inline void * __attr_always_inline___
 mem_heap_alloc_block_store_size (size_t size) /**< required size */
 {
   if (unlikely (size == 0))
@@ -537,7 +537,7 @@ mem_heap_free_block (void *ptr, /**< pointer to beginning of data space of the b
 /**
  * Free block with stored size
  */
-void __attr_always_inline___
+inline void __attr_always_inline___
 mem_heap_free_block_size_stored (void *ptr) /**< pointer to the memory block */
 {
   mem_heap_free_t *const original_p = ((mem_heap_free_t *) ptr) - 1;

jerry-core/mem/mem-poolman.c

@@ -129,7 +129,7 @@ mem_pools_finalize (void)
  * @return pointer to allocated chunk, if allocation was successful,
  *         or NULL - if not enough memory.
  */
-void * __attribute__((hot)) __attr_always_inline___
+inline void * __attribute__((hot)) __attr_always_inline___
 mem_pools_alloc (void)
 {
 #ifdef MEM_GC_BEFORE_EACH_ALLOC