Skip version check for unreferenced and undefined symbol

No need to check version if symbol is unreferenced and undefined.

bfd/

	PR ld/20306
	* elflink.c (elf_link_check_versioned_symbol): Return false
	for unreferenced undefined symbol.

ld/testsuite/

	* testsuite/ld-gc/gc.exp: Run pr20306 test.
	* ld-gc/pr20306.c: New file.
	* ld-gc/pr20306.d: Likewise.

bfd/ChangeLog

@@ -1,3 +1,9 @@
+2016-06-28  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/20306
+	* elflink.c (elf_link_check_versioned_symbol): Return false
+	for unreferenced undefined symbol.
+
 2016-06-28  Nick Clifton  <nickc@redhat.com>
 
 	* elf32-bfin.c (bfin_adjust_dynamic_symbol): Fail if a COPY reloc

bfd/elflink.c

@@ -9053,7 +9053,8 @@ elf_link_check_versioned_symbol (struct bfd_link_info *info,
     case bfd_link_hash_undefined:
     case bfd_link_hash_undefweak:
       abfd = h->root.u.undef.abfd;
-      if ((abfd->flags & DYNAMIC) == 0
+      if (abfd == NULL
+	  || (abfd->flags & DYNAMIC) == 0
 	  || (elf_dyn_lib_class (abfd) & DYN_DT_NEEDED) == 0)
 	return FALSE;
       break;

ld/ChangeLog

@@ -1,3 +1,9 @@
+2016-06-28  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* testsuite/ld-gc/gc.exp: Run pr20306 test.
+	* ld-gc/pr20306.c: New file.
+	* ld-gc/pr20306.d: Likewise.
+
 2016-06-28  Nick Clifton  <nickc@redhat.com>
 
 	* testsuite/ld-elf/comm-data.exp: Expect comm-data2 test to fail

ld/testsuite/ld-gc/gc.exp

@@ -146,3 +146,18 @@ if { [is_remote host] || [which $CC] != 0 } {
     ld_compile "$CC $CFLAGS $cflags -O0" $srcdir/$subdir/pr19161-2.c tmpdir/pr19161-2.o
     run_dump_test "pr19161"
 }
+
+if { [is_elf_format] && [check_shared_lib_support] \
+     && ([is_remote host] || [which $CC] != 0) } {
+    run_cc_link_tests [list \
+	[list \
+	    "Build libpr20306.so" \
+	    "-shared" \
+	    "-fPIC" \
+	    {pr20306.c} \
+	    {} \
+	    "libpr20306.so" \
+	] \
+    ]
+    run_dump_test "pr20306"
+}

ld/testsuite/ld-gc/pr20306.c

@@ -0,0 +1,2 @@
+extern void foo();
+void bar() {foo();}

ld/testsuite/ld-gc/pr20306.d

@@ -0,0 +1,3 @@
+#source: dummy.s
+#ld: -u foo --gc-sections tmpdir/libpr20306.so
+#error: .* generated: undefined reference to `foo'