Have you searched the OptiX SDK 7.5.0 files for CUDA_NVRTC_FLAGS and CUDA_NVRTC_OPTIONS?
None of them is using a space between -std and c++11.
Are you perhaps just missing the = in -std=c++11?
I mean this in OptiX SDK 7.5.0\SDK\CMakeLists.txt
if(CMAKE_CXX_STANDARD EQUAL 11)
set(SAMPLES_NVRTC_CXX "-std=c++11")
else()
set(SAMPLES_NVRTC_CXX "")
endif()
set(CUDA_NVRTC_FLAGS ${SAMPLES_NVRTC_CXX} -arch ${CUDA_MIN_SM_COMPUTE_TARGET} -use_fast_math -lineinfo -default-device -rdc true -D__x86_64 CACHE STRING "Semi-colon delimit multiple arguments." FORCE)
Here’s a similar definition of the CUDA_NVRTC_OPTIONS with the -std=c++11
https://forums.developer.nvidia.com/t/compile-error-failed-to-create-pipeline-optix-with-no-further-information-in-logs/205189/3