[ELF] SHF_LINK_ORDER: replace Fatal with ErrAlways

In LLD_IN_TEST=2 mode, when a thread calls Fatal, there will be no
output even if the process exits with code 1. Change the Fatal to
ErrAlways (not-recoverable) as subsequent code assumes SHF_LINK_ORDER
sh_link is correct.

Author: MaskRay

lld/ELF/InputFiles.cpp

@@ -890,9 +890,11 @@ void ObjFile<ELFT>::initializeSections(bool ignoreComdats,
     InputSectionBase *linkSec = nullptr;
     if (sec.sh_link < size)
       linkSec = this->sections[sec.sh_link];
-    if (!linkSec)
-      Fatal(ctx) << this
-                 << ": invalid sh_link index: " << uint32_t(sec.sh_link);
+    if (!linkSec) {
+      ErrAlways(ctx) << this
+                     << ": invalid sh_link index: " << uint32_t(sec.sh_link);
+      continue;
+    }
 
     // A SHF_LINK_ORDER section is discarded if its linked-to section is
     // discarded.

lld/test/ELF/invalid/linkorder-invalid-sec.test

@@ -1,6 +1,6 @@
 # REQUIRES: x86
 # RUN: yaml2obj %s -o %t.o
-# RUN: not ld.lld %t.o -o /dev/null 2>&1 | FileCheck %s
+# RUN: not ld.lld %t.o -o /dev/null --noinhibit-exec 2>&1 | FileCheck %s
 # CHECK: invalid sh_link index: 12345
 
 --- !ELF