[CMake] Change target 'check' from 'check-llvm' to 'check-all'

[mehdi_amini]

LGTM: I assume this is no change when only LLVM is configured, but it provides a better default otherwise right?

[echristo]

That's my perspective too and seems to make sense. People that need just check-llvm will have to be explicit now.

llvm/test/CMakeLists.txt

add_lit_testsuite(check-llvm "Running the LLVM regression tests"
   )
 set_target_properties(check-llvm PROPERTIES FOLDER "Tests")
 
 add_lit_testsuites(LLVM ${CMAKE_CURRENT_SOURCE_DIR}
   ${exclude_from_check_all}
   DEPENDS ${LLVM_TEST_DEPENDS}
   )
 
-# Setup a legacy alias for 'check-llvm'. This will likely change to be an
-# alias for 'check-all' at some point in the future.
+# Setup an alias for 'check-all'.
 add_custom_target(check)
-add_dependencies(check check-llvm)
+add_dependencies(check check-all)
 set_target_properties(check PROPERTIES FOLDER "Tests")