[compiler.h] add __USED to all __SECTION entries
This keeps the compiler from eliding things that are explicitly placed
in particular sections that it thinks aren't used.
#define __ALIGNED(x) __attribute__((aligned(x)))
#define __PRINTFLIKE(__fmt,__varargs) __attribute__((__format__ (__printf__, __fmt, __varargs)))
#define __SCANFLIKE(__fmt,__varargs) __attribute__((__format__ (__scanf__, __fmt, __varargs)))
-#define __SECTION(x) __attribute((section(x)))
+#define __SECTION(x) __USED __attribute((section(x)))
#define __PURE __attribute((pure))
#define __CONST __attribute((const))
#define __NO_RETURN __attribute__((noreturn))
