[CUDA] Define __CUDACC__ before standard library headers

libstdc++ since version 7 when GNU extensions are enabled (e.g. -std=gnu++11)
use it to avoid defining overloads using `__float128`.  This fixes compiling
with GNU extensions failing due to `__float128` being used.

Discovered at https://gitlab.kitware.com/cmake/cmake/-/merge_requests/4442#note_737136.

Differential Revision: https://reviews.llvm.org/D78392