libc-symbols.h: fix weak functions handling

Move weak_function and weak_const_function under HAVE_WEAK_SYMBOLS guard
and provide fallbacks.

Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

include/libc-symbols.h

@@ -196,12 +196,12 @@
 # define _strong_alias_untyped(name, aliasname) \
   extern __typeof (aliasname) aliasname __attribute__ ((alias (#name)));
 
+# ifdef HAVE_WEAK_SYMBOLS
+
 /* This comes between the return type and function name in
    a function definition to make that definition weak.  */
-# define weak_function __attribute__ ((weak))
-# define weak_const_function __attribute__ ((weak, __const__))
-
-# ifdef HAVE_WEAK_SYMBOLS
+#  define weak_function __attribute__ ((weak))
+#  define weak_const_function __attribute__ ((weak, __const__))
 
 /* Define ALIASNAME as a weak alias for NAME.
    If weak aliases are not available, this defines a strong alias.  */
@@ -215,6 +215,9 @@
 
 # else
 
+#  define weak_function /* empty */
+#  define weak_const_function __attribute__ ((__const__))
+
 #  define weak_alias(name, aliasname) strong_alias(name, aliasname)
 #  define weak_extern(symbol) /* Nothing. */