[openmp] Allow x87 fp functions only in Openmp runtime for x86.

This patch allows Openmp runtime atomic functions operating on x87 high-precision
to be present only in Openmp runtime for x86 architectures

The functions affected are:

__kmpc_atomic_10
__kmpc_atomic_20
__kmpc_atomic_cmplx10_add
__kmpc_atomic_cmplx10_div
__kmpc_atomic_cmplx10_mul
__kmpc_atomic_cmplx10_sub
__kmpc_atomic_float10_add
__kmpc_atomic_float10_div
__kmpc_atomic_float10_mul
__kmpc_atomic_float10_sub

__kmpc_atomic_float10_add_fp
__kmpc_atomic_float10_div_fp
__kmpc_atomic_float10_mul_fp
__kmpc_atomic_float10_sub_fp
__kmpc_atomic_float10_max
__kmpc_atomic_float10_min

Differential Revision: https://reviews.llvm.org/D117473