[LLD][COFF] Move entry thunk offset writing to writeSections (NFC) (#151254)

To make it easier to add entry thunks to other chunk types.

Author: cjacek

lld/COFF/Chunks.cpp

@@ -422,12 +422,6 @@ void SectionChunk::writeTo(uint8_t *buf) const {
 
     applyRelocation(buf + rel.VirtualAddress, rel);
   }
-
-  // Write the offset to EC entry thunk preceding section contents. The low bit
-  // is always set, so it's effectively an offset from the last byte of the
-  // offset.
-  if (Defined *entryThunk = getEntryThunk())
-    write32le(buf - sizeof(uint32_t), entryThunk->getRVA() - rva + 1);
 }
 
 void SectionChunk::applyRelocation(uint8_t *off,

lld/COFF/Writer.cpp

@@ -2544,7 +2544,15 @@ void Writer::writeSections() {
     }
 
     parallelForEach(sec->chunks, [&](Chunk *c) {
-      c->writeTo(secBuf + c->getRVA() - sec->getRVA());
+      uint8_t *buf = secBuf + c->getRVA() - sec->getRVA();
+      c->writeTo(buf);
+
+      // Write the offset to EC entry thunk preceding section contents. The low
+      // bit is always set, so it's effectively an offset from the last byte of
+      // the offset.
+      if (Defined *entryThunk = c->getEntryThunk())
+        write32le(buf - sizeof(uint32_t),
+                  entryThunk->getRVA() - c->getRVA() + 1);
     });
   }
 }