[fix] CMake 3.31+ breaks OpenMP detection in CUDA projects (issue #333)

[edenfunf]

What's the problem

CMake 3.31 added support for finding OpenMP in the CUDA language. When find_package(OpenMP) (or find_package(OpenMP REQUIRED)) is called inside a project that declares LANGUAGES C CXX CUDA, CMake now also tries to find OpenMP for CUDA. That lookup fails on most setups because nvcc doesn't expose OpenMP the same way GCC/Clang does:

CMake Error at .../FindPackageHandleStandardArgs.cmake:233 (message):
  Could NOT find OpenMP_CUDA (missing: OpenMP_CUDA_FLAGS OpenMP_CUDA_LIB_NAMES)
Call Stack:
  Samples/0_Introduction/UnifiedMemoryStreams/CMakeLists.txt:21 (find_package)

This hits anyone on CMake >= 3.31 building UnifiedMemoryStreams (and potentially cudaOpenMP) on Linux.

Steps to reproduce

cmake -S . -B build   # CMake >= 3.31 required

Error appears when CMake processes Samples/0_Introduction/UnifiedMemoryStreams/CMakeLists.txt.

What I changed

Samples/0_Introduction/UnifiedMemoryStreams/CMakeLists.txt

The Visual Studio branch already had find_package(OpenMP REQUIRED C CXX) — the non-VS branch was missing the language restriction. Since both cases want the same thing, I collapsed the if/else into a single call with C CXX specified:

# before
if(CMAKE_GENERATOR MATCHES "Visual Studio")
    find_package(OpenMP REQUIRED C CXX)
else()
    find_package(OpenMP REQUIRED)
endif()

# after
find_package(OpenMP REQUIRED C CXX)

Samples/0_Introduction/cudaOpenMP/CMakeLists.txt

Same root cause. find_package(OpenMP) without components in a CUDA project will attempt CUDA OpenMP detection on CMake 3.31+. Added C CXX here too:

# before
find_package(OpenMP)

# after
find_package(OpenMP C CXX)

Why this is safe

Specifying C CXX explicitly tells CMake "only look for OpenMP for these two languages." This is exactly what these samples need — they link against OpenMP::OpenMP_CXX and never use CUDA OpenMP. The behavior is identical on CMake < 3.31 since CUDA was not a recognized OpenMP language before that version.

Impact

Only affects the two sample CMakeLists files. No source code changes, no behavior change at runtime. Doesn't touch any other samples.

Fixes #333