Fix another --gc-sections crash.

The missing case was when a merge section was only referenced from
non-alloca sections.

llvm-svn: 282847

lld/ELF/InputSection.cpp

@@ -620,6 +620,9 @@ typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) const {
   if (It != OffsetMap.end())
     return It->second;
 
+  if (!this->Live)
+    return 0;
+
   // If Offset is not at beginning of a section piece, it is not in the map.
   // In that case we need to search from the original section piece vector.
   const SectionPiece &Piece = *this->getSectionPiece(Offset);

lld/test/ELF/gc-sections-non-alloc-to-merge.s

@@ -17,5 +17,11 @@ _start:
 .Lbar:
         .long 2
 
+        .section        .merge2,"aM",@progbits,4
+        .p2align        2
+.Lzed:
+        .long 1
+
         .section bar
         .quad .Lbar
+	.quad .Lzed