Start of series of patches with x86_64 vector math functions.

Start of series of patches with x86_64 vector math functions.

Here is implementation of cos containing SSE, AVX, AVX2 and AVX512
versions according to Vector ABI which had been discussed in
<https://groups.google.com/forum/#!topic/x86-64-abi/LmppCfN1rZ4>.

Vector math library build and ABI testing enabled by default for x86_64.

    * sysdeps/x86_64/fpu/Makefile: New file.
    * sysdeps/x86_64/fpu/Versions: New file.
    * sysdeps/x86_64/fpu/svml_d_cos_data.S: New file.
    * sysdeps/x86_64/fpu/svml_d_cos_data.h: New file.
    * sysdeps/x86_64/fpu/svml_d_cos2_core.S: New file.
    * sysdeps/x86_64/fpu/svml_d_cos4_core.S: New file.
    * sysdeps/x86_64/fpu/svml_d_cos4_core_avx.S: New file.
    * sysdeps/x86_64/fpu/svml_d_cos8_core.S: New file.
    * sysdeps/x86_64/fpu/svml_d_wrapper_impl.h: New file.
    * sysdeps/x86_64/fpu/multiarch/svml_d_cos2_core.S: New file.
    * sysdeps/x86_64/fpu/multiarch/svml_d_cos2_core_sse4.S: New file.
    * sysdeps/x86_64/fpu/multiarch/svml_d_cos4_core.S: New file.
    * sysdeps/x86_64/fpu/multiarch/svml_d_cos4_core_avx2.S: New file.
    * sysdeps/x86_64/fpu/multiarch/svml_d_cos8_core.S: New file.
    * sysdeps/x86_64/fpu/multiarch/svml_d_cos8_core_avx512.S: New file.
    * sysdeps/x86_64/fpu/multiarch/Makefile (libmvec-sysdep_routines): Added
    build of SSE, AVX2 and AVX512 IFUNC versions.
    * sysdeps/x86/fpu/bits/math-vector.h: Added SIMD declaration for cos.
    * math/bits/mathcalls.h: Added cos declaration with __MATHCALL_VEC.
    * sysdeps/x86_64/configure.ac: Options for libmvec build.
    * sysdeps/x86_64/configure: Regenerated.
    * sysdeps/x86_64/sysdep.h (cfi_offset_rel_rsp): New macro.
    * sysdeps/unix/sysv/linux/x86_64/libmvec.abilist: New file.
    * manual/install.texi (Configuring and compiling): Document
    --disable-mathvec.
    * INSTALL: Regenerated.
    * NEWS: Mention addition of libmvec and x86_64 vector cos.