Name each thunk symbol unique name

Previously, if symbol `foo` appears more than once in multiple thunks,
they got the same name `foo$thunk`. Now, they are named `foo$thunk0`,
etc.

src/mold.h

@@ -117,6 +117,7 @@ class Thunk<E> {
   OutputSection<E> &output_section;
   i64 offset;
   std::vector<Symbol<E> *> symbols;
+  std::string name;
 };
 
 template <needs_thunk E>

src/output-chunks.cc

@@ -1185,7 +1185,7 @@ void OutputSection<E>::compute_symtab_size(Context<E> &ctx) {
         this->num_local_symtab += thunk->symbols.size();
 
       for (Symbol<E> *sym : thunk->symbols)
-        this->strtab_size += sym->name().size() + sizeof("$thunk");
+        this->strtab_size += sym->name().size() + thunk->name.size() + 2;
     }
   }
 }
@@ -1219,7 +1219,8 @@ void OutputSection<E>::populate_symtab(Context<E> &ctx) {
         write_esym(addr, strtab - strtab_base);
 
         strtab += write_string(strtab, sym.name()) - 1;
-        strtab += write_string(strtab, "$thunk");
+        *strtab++ = '$';
+        strtab += write_string(strtab, thunk->name);
 
         // Emit "$t", "$a" and "$d" if ARM32.
         if constexpr (is_arm32<E>) {

src/passes.cc

@@ -1754,6 +1754,14 @@ template <typename E>
 void create_output_symtab(Context<E> &ctx) {
   Timer t(ctx, "compute_symtab_size");
 
+  if constexpr (needs_thunk<E>) {
+    i64 n = 0;
+    for (Chunk<E> *chunk : ctx.chunks)
+      if (OutputSection<E> *osec = chunk->to_osec())
+        for (std::unique_ptr<Thunk<E>> &thunk : osec->thunks)
+          thunk->name = "thunk" + std::to_string(n++);
+  }
+
   tbb::parallel_for_each(ctx.chunks, [&](Chunk<E> *chunk) {
     chunk->compute_symtab_size(ctx);
   });

test/arch-aarch64-range-extension-thunk-disassembly.sh

@@ -18,4 +18,4 @@ EOF
 $CC -B. -o $t/exe $t/a.o \
   -Wl,--section-start=.low=0x10000000,--section-start=.high=0x20000000
 
-$OBJDUMP -dr $t/exe | grep -Fq '<fn1$thunk>:'
+$OBJDUMP -dr $t/exe | grep -Eq '<fn1\$thunk[0-9]+>:'

test/arch-arm-range-extension-thunk-disassembly.sh

@@ -18,7 +18,7 @@ EOF
 $CC -B. -o $t/exe $t/a.o \
   -Wl,--section-start=.low=0x10000000,--section-start=.high=0x20000000
 
-$OBJDUMP -dr $t/exe | grep -F -A7 '<fn1$thunk>:' > $t/log
+$OBJDUMP -dr $t/exe | grep -E -A7 '<fn1\$thunk[0-9]+>:' > $t/log
 
 grep -Eq 'bx\s+pc' $t/log
 grep -Eq 'add\s+pc, ip, pc' $t/log