Use memcpy for possibly-unaligned loads and stores.

The core change is ported from
BLAKE2/BLAKE2@b8024d5.

This let's us remove the ALIGNED_ACCESS_REQUIRED configure check. This isn't a
very good thing to check through configure because it requires running an
executable. That doesn't work for cross compiles.

configure.ac

@@ -17,7 +17,6 @@ AC_CHECK_FUNCS(explicit_memset)
 AC_CHECK_FUNCS(memset_s)
 AC_CHECK_HEADERS([stddef.h stdint.h stdlib.h string.h])
 AC_OPENMP
-AX_CHECK_ALIGNED_ACCESS_REQUIRED
 # AX_FORCEINLINE()
 AC_C_BIGENDIAN(
 	[],

src/blake2-impl.h

@@ -29,8 +29,10 @@
 
 static inline uint32_t load32( const void *src )
 {
-#if defined(NATIVE_LITTLE_ENDIAN) && !defined(HAVE_ALIGNED_ACCESS_REQUIRED)
-  return *( uint32_t * )( src );
+#if defined(NATIVE_LITTLE_ENDIAN)
+  uint32_t w;
+  memcpy( &w, src, sizeof( w ) );
+  return w;
 #else
   const uint8_t *p = ( uint8_t * )src;
   uint32_t w = *p++;
@@ -43,8 +45,10 @@ static inline uint32_t load32( const void *src )
 
 static inline uint64_t load64( const void *src )
 {
-#if defined(NATIVE_LITTLE_ENDIAN) && !defined(HAVE_ALIGNED_ACCESS_REQUIRED)
-  return *( uint64_t * )( src );
+#if defined(NATIVE_LITTLE_ENDIAN)
+  uint64_t w;
+  memcpy( &w, src, sizeof( w ) );
+  return w;
 #else
   const uint8_t *p = ( uint8_t * )src;
   uint64_t w = *p++;
@@ -61,8 +65,8 @@ static inline uint64_t load64( const void *src )
 
 static inline void store32( void *dst, uint32_t w )
 {
-#if defined(NATIVE_LITTLE_ENDIAN) && !defined(HAVE_ALIGNED_ACCESS_REQUIRED)
-  *( uint32_t * )( dst ) = w;
+#if defined(NATIVE_LITTLE_ENDIAN)
+  memcpy( dst, &w, sizeof( w ) );
 #else
   uint8_t *p = ( uint8_t * )dst;
   *p++ = ( uint8_t )w; w >>= 8;
@@ -74,8 +78,8 @@ static inline void store32( void *dst, uint32_t w )
 
 static inline void store64( void *dst, uint64_t w )
 {
-#if defined(NATIVE_LITTLE_ENDIAN) && !defined(HAVE_ALIGNED_ACCESS_REQUIRED)
-  *( uint64_t * )( dst ) = w;
+#if defined(NATIVE_LITTLE_ENDIAN)
+  memcpy( dst, &w, sizeof( w ) );
 #else
   uint8_t *p = ( uint8_t * )dst;
   *p++ = ( uint8_t )w; w >>= 8;