Revert "fix(ld.so): temporary rollback"

This reverts commit 5cf865189d.

src/ld_so/dso.rs

@@ -534,7 +534,7 @@ impl DSO {
                 let size = end - start;
                 let mut flags = sys_mman::MAP_ANONYMOUS | sys_mman::MAP_PRIVATE;
                 if start != 0 {
-                    flags |= sys_mman::MAP_FIXED;
+                    flags |= sys_mman::MAP_FIXED_NOREPLACE;
                 }
                 log::trace!("  mmap({:#x}, {:x}, {:x})", start, size, flags);
                 let ptr = Sys::mmap(

src/ld_so/start.rs

@@ -286,7 +286,7 @@ pub unsafe extern "C" fn relibc_ld_so_start(
     }
 
     let mut base_addr = None;
-    if !is_manual && cfg!(not(target_os = "redox")) {
+    if !is_manual {
         // if we are not running in manual mode, then the main
         // program is already loaded by the kernel and we want
         // to use it. on redox, we treat it the same.