pmmintrin.h documentation fixes and updates

[dyung]

Summary

This is the result of several patches we made internally to update the documentation that we would like to have reviewed for possible submission.

The changes include:

1. Fix incorrect wording in various intrinsic descriptions. Previously the descriptions used "low-order" and "high-order" when the intended meaning was "even-indexed" and "odd-indexed".

These patches were made by Craig Flores

[RKSimon]

LGTM

lib/Headers/pmmintrin.h

 /// \returns A 128-bit vector of [4 x float] containing the horizontal
 ///    differences of both operands.
 static __inline__ __m128 __DEFAULT_FN_ATTRS
 _mm_hsub_ps(__m128 __a, __m128 __b)
 {
   return __builtin_ia32_hsubps((__v4sf)__a, (__v4sf)__b);
 }
 
-/// \brief Moves and duplicates high-order (odd-indexed) values from a 128-bit
-///    vector of [4 x float] to float values stored in a 128-bit vector of
+/// \brief Moves and duplicates odd-indexed values from a 128-bit vector
+///    of [4 x float] to float values stored in a 128-bit vector of
 ///    [4 x float].
 ///
 /// \headerfile <x86intrin.h>
 ///
 /// This intrinsic corresponds to the <c> VMOVSHDUP </c> instruction.
 ///
 /// \param __a
 ///    A 128-bit vector of [4 x float]. \n
 ///    Bits [127:96] of the source are written to bits [127:96] and [95:64] of
 ///    the destination. \n
 ///    Bits [63:32] of the source are written to bits [63:32] and [31:0] of the
 ///    destination.
 /// \returns A 128-bit vector of [4 x float] containing the moved and duplicated
 ///    values.
 static __inline__ __m128 __DEFAULT_FN_ATTRS
 _mm_movehdup_ps(__m128 __a)
 {
   return __builtin_shufflevector((__v4sf)__a, (__v4sf)__a, 1, 1, 3, 3);
 }
 
-/// \brief Duplicates low-order (even-indexed) values from a 128-bit vector of
+/// \brief Duplicates even-indexed values from a 128-bit vector of
 ///    [4 x float] to float values stored in a 128-bit vector of [4 x float].
 ///
 /// \headerfile <x86intrin.h>
 ///
 /// This intrinsic corresponds to the <c> VMOVSLDUP </c> instruction.
 ///
 /// \param __a
 ///    A 128-bit vector of [4 x float] \n