x86-64: Align L(SP_RANGE)/L(SP_INF_0) to 8 bytes [BZ #21955]

sysdeps/x86_64/fpu/e_expf.S has

        lea     L(SP_RANGE)(%rip), %rdx /* load over/underflow bound */
        cmpl    (%rdx,%rax,4), %ecx     /* |x|<under/overflow bound ? */
...
        /* Here if |x| is Inf */
        lea     L(SP_INF_0)(%rip), %rdx /* depending on sign of x: */
        movss   (%rdx,%rax,4), %xmm0    /* return zero or Inf */
        ret
...
         .section .rodata.cst8,"aM",@progbits,8
...
        .p2align 2
L(SP_RANGE): /* single precision overflow/underflow bounds */
        .long   0x42b17217      /* if x>this bound, then result overflows */
        .long   0x42cff1b4      /* if x<this bound, then result underflows */
        .type L(SP_RANGE), @object
        ASM_SIZE_DIRECTIVE(L(SP_RANGE))

        .p2align 2
L(SP_INF_0):
        .long   0x7f800000      /* single precision Inf */
        .long   0               /* single precision zero */
        .type L(SP_INF_0), @object
        ASM_SIZE_DIRECTIVE(L(SP_INF_0))

Since L(SP_RANGE) and L(SP_INF_0) are in .rodata.cst8 section, they must
be aligned to 8 bytes.

	[BZ #21955]
	* sysdeps/x86_64/fpu/e_expf.S (L(SP_RANGE)): Aligned to 8 bytes.
	(L(SP_INF_0)): Likewise.