Prevent runtime fail of SSE vector math tests on non SSE4.1 machine.

    [BZ #18740]
    * sysdeps/x86_64/fpu/Makefile (double-vlen2-arch-ext-cflags,
    float-vlen4-arch-ext-cflags): Removed.
    * math/Makefile (CFLAGS-test-double-vlen2-wrappers.c,
    CFLAGS-test-float-vlen4-wrappers.c): Likewise.