[ELF] Fix symbol resolution for versioned symbols

My last commit d391fd9a59 changes how we
resolve versioned symbols, but that affected too many programs.
In particular it broke GCC build, so reverted in
f378fdc495.

This commit is an attempt to fix the same issue with a minimal change.

Fixes https://github.com/rui314/mold/issues/475

elf/passes.cc

@@ -1121,10 +1121,13 @@ void parse_symbol_version(Context<E> &ctx) {
 
       // If both symbol `foo` and `foo@VERSION` are defined, `foo@VERSION`
       // hides `foo` so that all references to `foo` are resolved to a
-      // versioned symbol.
+      // versioned symbol. Likewise, if `foo@VERSION` and `foo@@VERSION` are
+      // defined, the default one takes precedence.
       Symbol<E> *sym2 = get_symbol(ctx, sym->name());
       if (sym2->file == file && !file->symvers[sym2->sym_idx - file->first_global])
-        sym2->ver_idx = VER_NDX_LOCAL;
+        if (sym2->ver_idx == ctx.default_version ||
+            (sym2->ver_idx & ~VERSYM_HIDDEN) == (sym->ver_idx & ~VERSYM_HIDDEN))
+          sym2->ver_idx = VER_NDX_LOCAL;
     }
   });
 }

test/elf/symbol-version3.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+export LC_ALL=C
+set -e
+CC="${CC:-cc}"
+CXX="${CXX:-c++}"
+GCC="${GCC:-gcc}"
+GXX="${GXX:-g++}"
+OBJDUMP="${OBJDUMP:-objdump}"
+MACHINE="${MACHINE:-$(uname -m)}"
+testname=$(basename "$0" .sh)
+echo -n "Testing $testname ... "
+cd "$(dirname "$0")"/../..
+mold="$(pwd)/mold"
+t=out/test/elf/$testname
+mkdir -p $t
+
+cat <<EOF | $CC -o $t/a.o -c -xc -
+void foo() {}
+void foo2() {}
+void foo3() {}
+
+__asm__(".symver foo2, foo@TEST2");
+__asm__(".symver foo3, foo@TEST3");
+EOF
+
+cat <<EOF > $t/b.version
+TEST1 { global: foo; };
+TEST2 {};
+TEST3 {};
+EOF
+
+$CC -B. -o $t/c.so -shared $t/a.o -Wl,--version-script=$t/b.version
+readelf -W --dyn-syms $t/c.so > $t/log
+
+grep -q ' foo@@TEST1$' $t/log
+grep -q ' foo@TEST2$' $t/log
+grep -q ' foo@TEST3$' $t/log
+! grep -q ' foo$' $t/log || false
+
+echo OK