Include some test.exec tests in the modules build

This diff moves the special-casing of `test.exec` down into the nearest
`CMakeLists.txt` file; most of the tests in `test/exec` don't build, but
a couple of them do.

Author: ispeters

test/CMakeLists.txt

@@ -171,10 +171,7 @@ if(STDEXEC_BUILD_PARALLEL_SCHEDULER AND NOT STDEXEC_ENABLE_CUDA)
                        30)
 endif()
 
-if(NOT STDEXEC_BUILD_MODULES)
-    # temporarily speed up the test cycle by building less
-    add_subdirectory(exec)
-endif()
+add_subdirectory(exec)
 
 if(STDEXEC_ENABLE_CUDA)
   add_subdirectory(nvexec)

test/exec/CMakeLists.txt

@@ -70,9 +70,15 @@ set_source_files_properties(
   test_any_sender.cpp PROPERTIES COMPILE_FLAGS
                                  $<$<CXX_COMPILER_ID:MSVC>:/bigobj>)
 
-add_executable(test.exec ${exec_test_sources})
 if(STDEXEC_BUILD_MODULES)
+  # these are the only files that build right now...
+  add_executable(test.exec
+      ../test_main.cpp
+      async_scope/test_empty.cpp
+      async_scope/test_spawn.cpp)
   set_target_properties(test.exec PROPERTIES CXX_MODULE_STD ON)
+else()
+  add_executable(test.exec ${exec_test_sources})
 endif()
 
 add_compile_diagnostics(test.exec)