MFC 262989, 263210, 263230, 263231, 263239, 263242, 263243,

MFC 262989, 263210, 263230, 263231, 263239, 263242, 263243,

  Export _libc_arm_fpu_present as a private symbol to be used by other
  system libraries, for example libm.

  On armv6 access both the softfloat and, when available, the vfp to get and
  set the floating-point environment.

  Build fenv-vfp.c with the softfp float abi. Without this gcc generates an
  incorrect assembly file that doesn't allow for vfp instructions.

  Only build the vfp/softfp switching code on armv6 as we don't support vfp
  on anything earlier than this. This should fix the armeb and arm builds
  when using gcc.

  Add an optimised version of the float and double helper functions.

git-svn-id: svn://svn.freebsd.org/base/stable/10@266314 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f