Addition of testing infrastructure for vector math functions.

Addition of testing infrastructure for vector math functions.

We test vector math functions using scalar tests infrastructure with
help of special wrappers from scalar versions to vector ones. Wrapper
implemented using platform specific vector types and placed in separate
file for compilation with architecture specific options, main part of
test has no such options. With help of system of definitions unfolding
of which is drived from test code we have wrapper called in individual
testing function instead of scalar function. Also system of definitions
includes generated during make check header math/libm-have-vector-test.h
with series of conditional definitions which help to avoid build fails
for functions having no vector versions; runtime architecture check
to prevent runtime fails of test run on inappropriate hardware.

    * math/Makefile: Added rules for vector tests.
    * math/gen-libm-have-vector-test.sh: Added generation of wrapper
    declaration under condition.
    * math/test-double-vlen2.h: New file.
    * math/test-double-vlen4.h: New file.
    * math/test-double-vlen8.h: New file.
    * math/test-vec-loop.h: Added initialization macro.
    * sysdeps/x86_64/fpu/Makefile: Added variables for vector tests.
    * sysdeps/x86_64/fpu/libm-test-ulps: Regenarated.
    * sysdeps/x86_64/fpu/math-tests-arch.h: New file.
    * sysdeps/x86_64/fpu/test-double-vlen2-wrappers.c: New file.
    * sysdeps/x86_64/fpu/test-double-vlen2.c: New file.
    * sysdeps/x86_64/fpu/test-double-vlen4-avx2-wrappers.c: New file.
    * sysdeps/x86_64/fpu/test-double-vlen4-avx2.c: New file.
    * sysdeps/x86_64/fpu/test-double-vlen4-wrappers.c: New file.
    * sysdeps/x86_64/fpu/test-double-vlen4.c: New file.
    * sysdeps/x86_64/fpu/test-double-vlen8-wrappers.c: New file.
    * sysdeps/x86_64/fpu/test-double-vlen8.c: New file.