implement "low hanging fruit" from C11

based on Gregor's patch sent to the list. includes:
- stdalign.h
- removing gets in C11 mode
- adding aligned_alloc and adjusting other functions to use it
- adding 'x' flag to fopen for exclusive mode

include/stdio.h

@@ -90,7 +90,9 @@ int putc(int, FILE *);
 int putchar(int);
 
 char *fgets(char *, int, FILE *);
+#if __STDC_VERSION__ < 201112L
 char *gets(char *);
+#endif
 
 int fputs(const char *, FILE *);
 int puts(const char *);