clang/llvm 9 fix - do not eliminate a store to a fake "const"

This is *much* better (9 kbytes better) than dropping "*const"
optimization trick.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libbb/appletlib.c

@@ -304,7 +304,7 @@ void lbb_prepare(const char *applet
 		IF_FEATURE_INDIVIDUAL(, char **argv))
 {
 #ifdef __GLIBC__
-	(*(int **)&bb_errno) = __errno_location();
+	(*(int **)not_const_pp(&bb_errno)) = __errno_location();
 	barrier();
 #endif
 	applet_name = applet;