Add support for init/fini arrays to libc (#1725)

The arrays contain the addresses of functions annotated with
constructor or destructor attributes. The support is optional,
requires FEATURE_INIT_FINI cmake option to be set. As of now, the
option is _not_ available in tools/build.py directly, only via
`--cmake-param="-DFEATURE_INIT_FINI=ON"`.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

jerry-libc/jerry-libc-defs.h

@@ -27,5 +27,11 @@
 #define __attr_used___     __attribute__((used))
 #define __attr_noreturn___ __attribute__((noreturn))
 #define __attr_noinline___ __attribute__((noinline))
+#define __attr_weak___     __attribute__((weak))
+
+#ifdef ENABLE_INIT_FINI
+void libc_init_array (void);
+void libc_fini_array (void);
+#endif /* ENABLE_INIT_FINI */
 
 #endif /* !DEFS_H */