Refactoring of START for conditions in individual tests

Refactoring of START for conditions in individual tests
and addition of macros used for runtime architecture check.

2015-04-28  Andrew Senkevich  <andrew.senkevich@intel.com>

    * math/libm-test.inc: START refactored.
    * math/test-double.c (TEST_MATHVEC): Add define.
    * math/test-float.c: Likewise.
    * math/test-idouble.c: Likewise.
    * math/test-ifloat.c: Likewise.
    * math/test-ildoubl.c: Likewise.
    * math/test-ldouble.c: Likewise.
    * sysdeps/generic/math-tests-arch.h (INIT_ARCH_EXT, CHECK_ARCH_EXT):
    New helper macros for runtime architecture check.