x86-64: Add a test for hidden undefined symbol

x86-64: Add a test for hidden undefined symbol

Linker should report an error for hidden undefined symbol when building
a shared library without the "recompile with -fPIC" message:

$ cat x.c
extern int foo __attribute__ ((visibility ("hidden")));

int
func (void)
{
  return foo;
}
$ gcc -c -fPIC -O2 x.c
$ objdump -dwr x.o

x.o:     file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <func>:
   0:	8b 05 00 00 00 00    	mov    0x0(%rip),%eax        # 6 <func+0x6>	2: R_X86_64_PC32	foo-0x4
   6:	c3                   	ret
$ ld -shared -o x.so x.o
ld: x.o: in function `func':
x.c:(.text+0x2): undefined reference to `foo'
ld: x.o: relocation R_X86_64_PC32 against undefined hidden symbol `foo' can not be used when making a shared object
ld: final link failed: bad value
$

since -fPIC has been used.

	* testsuite/ld-x86-64/hidden6.d: New file.
	* testsuite/ld-x86-64/hidden6.s: Likewise.
	* testsuite/ld-x86-64/x86-64.exp: Run hidden6.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>