CUDA: Fail if compiler detection using the host compiler fails

If an user specified a host compiler we should fail if we are unable to perform
compiler detection with it.
Previously we would try without and likely succeed and continue. Then we'd fail
during ABI detection and compiler testing since we'd still try to use it.

This is particularly problematic when crosscompiling since we extract the host
linker from the compiler detection link line. This would result in the wrong
host linker being used and a linking error due to architecture mismatch during
ABI detection where other necessary flags may already be present to make the
host compiler work. See #21076 for an example.

Fix this by adding CMAKE_<LANG>_COMPILER_ID_REQUIRE_SUCCESS to
CMakeDetermineCompilerId, which throws a fatal error if executing the compiler
results in a non-zero exit code.

Fixes #21120.

Help/release/dev/cuda-fail-fast.rst

@@ -0,0 +1,5 @@
+cuda-fail-fast
+--------------
+
+* If ``CUDA`` compiler detection fails with user-specified
+  :variable:`CMAKE_CUDA_ARCHITECTURES` an error is raised.

Modules/CMakeDetermineCUDACompiler.cmake

@@ -189,6 +189,10 @@ if(NOT CMAKE_CUDA_COMPILER_ID_RUN)
     set(nvcc_test_flags "--keep --keep-dir tmp")
     if(CMAKE_CUDA_HOST_COMPILER)
       string(APPEND nvcc_test_flags " -ccbin=\"${CMAKE_CUDA_HOST_COMPILER}\"")
+
+      # If the user has specified a host compiler we should fail instead of trying without.
+      # Succeeding detection without may result in confusing errors later on, see #21076.
+      set(CMAKE_CUDA_COMPILER_ID_REQUIRE_SUCCESS ON)
     endif()
   elseif(CMAKE_CUDA_COMPILER_ID STREQUAL "Clang")
     if(WIN32)

Modules/CMakeDetermineCompilerId.cmake

@@ -606,9 +606,12 @@ ${CMAKE_${lang}_COMPILER_ID_OUTPUT}
 
 ")
     file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log "${MSG}")
-    #if(NOT CMAKE_${lang}_COMPILER_ID_ALLOW_FAIL)
-    #  message(FATAL_ERROR "${MSG}")
-    #endif()
+
+    # Some languages may know the correct/desired set of flags and want to fail right away if they don't work.
+    # This is currently only used by CUDA.
+    if(CMAKE_${lang}_COMPILER_ID_REQUIRE_SUCCESS)
+      message(FATAL_ERROR "${MSG}")
+    endif()
 
     # No output files should be inspected.
     set(COMPILER_${lang}_PRODUCED_FILES)