make dynamic linker depend on -DSHARED not -fPIC

if libc.a is compiled PIC for use in static PIE code, this should not
cause the dynamic linker (which still does not support static-linked
main program) to be built into libc.a.

src/ldso/dynlink.c

@@ -20,7 +20,7 @@
 static int errflag;
 static char errbuf[128];
 
-#ifdef __PIC__
+#ifdef SHARED
 
 #include "reloc.h"