headers: Add missing declaration for __mingw_aligned_offset_malloc()

There is already declaration for msvcrt _aligned_offset_malloc() function,
so add export also declaration for mingw __mingw_aligned_offset_malloc()
function.

At the same time, remove also uneeded declaration of this function from
mingw-w64-crt/misc/mingw-aligned-malloc.c file and use the new one from
malloc.h.

Signed-off-by: Martin Storsjö <martin@martin.st>

mingw-w64-crt/misc/mingw-aligned-malloc.c

diff --git a/mingw-w64-crt/misc/mingw-aligned-malloc.c b/mingw-w64-crt/misc/mingw-aligned-malloc.c
index ca5f866..5029b60 100644
--- a/mingw-w64-crt/misc/mingw-aligned-malloc.c
+++ b/mingw-w64-crt/misc/mingw-aligned-malloc.c
@@ -18,9 +18,6 @@
 #include <stdint.h>		/* uintptr_t */
 #include <string.h>		/* memmove */
 
-/* Forward declarations:  */
-void *__mingw_aligned_offset_malloc (size_t, size_t, size_t);
-
 #define NOT_POWER_OF_TWO(n) (((n) & ((n) - 1)))
 #define UI(p) ((uintptr_t) (p))
 #define CP(p) ((char *) p)

mingw-w64-headers/crt/malloc.h

diff --git a/mingw-w64-headers/crt/malloc.h b/mingw-w64-headers/crt/malloc.h
index 9c498c2..cc72d4c 100644
--- a/mingw-w64-headers/crt/malloc.h
+++ b/mingw-w64-headers/crt/malloc.h
@@ -131,6 +131,7 @@
 void * __mingw_aligned_malloc (size_t _Size, size_t _Alignment);
 void __mingw_aligned_free (void *_Memory);
 void * __mingw_aligned_offset_realloc (void *_Memory, size_t _Size, size_t _Alignment, size_t _Offset);
+void * __mingw_aligned_offset_malloc (size_t, size_t, size_t);
 void * __mingw_aligned_realloc (void *_Memory, size_t _Size, size_t _Offset);
 
 #if defined(__x86_64__) || defined(__i386__)