!66 在liteos_a内核C库中补充stdalign.h

Merge pull request !66 from Zhaotianyu/0726stdalign

porting/liteos_a/kernel/include/stdalign.h

+#ifndef _STDALIGN_H
+#define _STDALIGN_H
+
+#ifndef __cplusplus
+
+/* this whole header only works in C11 or with compiler extensions */
+#if __STDC_VERSION__ < 201112L && defined( __GNUC__)
+#undef _Alignas
+#define _Alignas(t) __attribute__((__aligned__(t)))
+#undef _Alignof
+#define _Alignof(t) __alignof__(t)
+#endif
+
+#define alignas _Alignas
+#define alignof _Alignof
+
+#endif
+
+#define __alignas_is_defined 1
+#define __alignof_is_defined 1
+
+#endif