Fix PR c++/64697 at -O1 or above

Fix PR c++/64697 at -O1 or above

The BFD fix eliminates the link failure and working code is generated at
-O0, but _not_ when optimization is enabled because the optimizer changes:

        movq    .refptr._ZTH1s(%rip), %rax
        testq   %rax, %rax
        je      .L2
        call    _ZTH1s

into:

        leaq    _ZTH1s(%rip), %rax
        testq   %rax, %rax
        je      .L2
        call    _ZTH1s

and the leaq now also gets the relocation overflow.  So the fix is to
teach legitimate_pic_address_disp_p to reject the transformation when
the symbol is an external weak function, which yields:

        cmpq    $0, .refptr._ZTH1s(%rip)
        je      .L2
        call    _ZTH1s

and the cmpq keeps a relocation that does not overflow.

gcc/
	PR c++/64697
	* config/i386/i386.c (legitimate_pic_address_disp_p): For PE-COFF do
	not return true for external weak function symbols in medium model.