add real fdpic loading of shared libraries

previously, the normal ELF library loading code was used even for
fdpic, so only the kernel-loaded dynamic linker and main app could
benefit from separate placement of segments and shared text.

src/internal/dynlink.h

@@ -56,6 +56,10 @@ struct fdpic_dummy_loadmap {
 
 #include "reloc.h"
 
+#ifndef FDPIC_CONSTDISP_FLAG
+#define FDPIC_CONSTDISP_FLAG 0
+#endif
+
 #ifndef DL_FDPIC
 #define DL_FDPIC 0
 #endif