[runtimes] Support sub-components in LLVM_RUNTIME_DISTRIBUTION_COMPONENTS

[smeenai]

Summary

Right now, sub-components are only accounted for when the runtime has
been configured and the main LLVM configure is rerun after that. We can
make use of LLVM_RUNTIME_DISTRIBUTION_COMPONENTS to make sub-component
targets available from the start, but that currently clashes with the
sub-component target generation once they are picked up. Make sure we
don't create duplicate targets; an analogous check already exists in
runtime_default_target.

[phosek]

LGTM

llvm/runtimes/CMakeLists.txt

function(runtime_register_target name target)
 
   foreach(target_name IN LISTS SUB_INSTALL_TARGETS)
     set(${target_name}-${name} ${target_name})
     set(${target_name}-${name}-stripped ${target_name}-stripped)
     list(APPEND ${name}_extra_targets ${target_name}-${name} ${target_name}-${name}-stripped)
   endforeach()
 
   foreach(component ${LLVM_RUNTIME_DISTRIBUTION_COMPONENTS})
+    if(NOT component IN_LIST SUB_COMPONENTS)
       set(${component}-${name} ${component})
       set(install-${component}-${name} install-${component})
       set(install-${component}-${name}-stripped install-${component}-stripped)
       list(APPEND ${name}_extra_targets ${component}-${name} install-${component}-${name} install-${component}-${name}-stripped)
+    endif()
   endforeach()
 
   if(LLVM_INCLUDE_TESTS)
     set_property(GLOBAL APPEND PROPERTY LLVM_ALL_LIT_TESTSUITES "@${LLVM_BINARY_DIR}/runtimes/runtimes-${name}-bins/lit.tests")
     set(runtimes-test-depends-${name} runtimes-test-depends)
     set(check-runtimes-${name} check-runtimes)
     list(APPEND ${name}_test_targets runtimes-test-depends-${name} check-runtimes-${name})
     list(APPEND test_targets ${${name}_test_targets})