Only generate per-dialect targets when needed.

cmake/ThrustBuildCompilerTargets.cmake

@@ -6,11 +6,9 @@
 # - Interface target providing compiler-specific options needed to build
 #   Thrust's tests, examples, etc.
 #
-# thrust.compiler_interface_cpp11
-# thrust.compiler_interface_cpp14
-# thrust.compiler_interface_cpp17
+# thrust.compiler_interface_cppXX
 # - Interface targets providing compiler-specific options that should only be
-#   applied to certain dialects of C++.
+#   applied to certain dialects of C++. May not be defined for all dialects.
 #
 # thrust.promote_cudafe_warnings
 # - Interface target that adds warning promotion for NVCC cudafe invocations.
@@ -175,7 +173,6 @@ function(thrust_build_compiler_targets)
   # These targets are used for dialect-specific options:
   add_library(thrust.compiler_interface_cpp11 INTERFACE)
   add_library(thrust.compiler_interface_cpp14 INTERFACE)
-  add_library(thrust.compiler_interface_cpp17 INTERFACE)
 
   if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
     # C4127: conditional expression is constant

cmake/ThrustBuildTargetList.cmake

@@ -163,9 +163,15 @@ function(_thrust_add_target_to_target_list target_name host device dialect prefi
 
   target_link_libraries(${target_name} INTERFACE
     thrust.compiler_interface
-    thrust.compiler_interface_cpp${dialect}
   )
 
+  # dialect-specific interface:
+  if (TARGET thrust.compiler_interface_cpp${dialect})
+    target_link_libraries(${target_name} INTERFACE
+      thrust.compiler_interface_cpp${dialect}
+    )
+  endif()
+
   # Workaround Github issue #1174. cudafe promote TBB header warnings to
   # errors, even when they're -isystem includes.
   if ((NOT host STREQUAL "TBB") OR (NOT device STREQUAL "CUDA"))