[CMake] Support runtimes in distributions

[beanz]

Summary

This patch adds a new internal variable
LLVM_RUNTIME_DISTRIBUTION_COMPONENTS which specifies distribution
components that are part of runtime projects, and thus should be exposed
from runtime configuraitons up into the top-level CMake configurations.

This is required for allowing runtime components to be included in
LLVM_DISTRIBUTION_COMPONENTS because we verify that the build and
install targets exist for every component specified for the
distribution.

Without this patch runtimes and builtins can only be included in
distributions in whole, not by component.

[phosek]

LGTM

CMakeLists.txt

 if(LLVM_DISTRIBUTION_COMPONENTS)
   if(CMAKE_CONFIGURATION_TYPES)
     message(FATAL_ERROR "LLVM_DISTRIBUTION_COMPONENTS cannot be specified with multi-configuration generators (i.e. Xcode or Visual Studio)")
   endif()
 
   add_custom_target(distribution)
   add_custom_target(install-distribution)
   add_custom_target(install-distribution-stripped)
-  foreach(target ${LLVM_DISTRIBUTION_COMPONENTS})
+  foreach(target ${LLVM_DISTRIBUTION_COMPONENTS} ${LLVM_RUNTIME_DISTRIBUTION_COMPONENTS})
     if(TARGET ${target})
       add_dependencies(distribution ${target})
     else()
       message(SEND_ERROR "Specified distribution component '${target}' doesn't have a target")
     endif()
 
     if(TARGET install-${target})
       add_dependencies(install-distribution install-${target})

runtimes/CMakeLists.txt

foreach(runtime_name ${runtime_names})
       list(APPEND extra_targets
         ${runtime_name}
         install-${runtime_name}
         install-${runtime_name}-stripped)
       if(LLVM_INCLUDE_TESTS)
         list(APPEND test_targets check-${runtime_name})
       endif()
     endforeach()
+    foreach(component ${LLVM_RUNTIME_DISTRIBUTION_COMPONENTS})
+      if(NOT ${component} IN_LIST SUB_COMPONENTS)
+        list(APPEND extra_targets ${component} install-${component} install-${component}-stripped)
+      endif()
+    endforeach()
 
     if(LLVM_INCLUDE_TESTS)
       list(APPEND test_targets runtimes-test-depends check-runtimes)
     endif()
 
     llvm_ExternalProject_Add(runtimes
                              ${CMAKE_CURRENT_SOURCE_DIR}
                              DEPENDS ${ARG_DEPS}
foreach(runtime_name ${runtime_names})
         list(APPEND ${name}_test_targets "check-${runtime_name}:check-${runtime_name}-${name}")
       endif()
     endforeach()
 
     foreach(target_name IN LISTS SUB_COMPONENTS SUB_INSTALL_TARGETS)
       list(APPEND ${name}_extra_targets "${target_name}:${target_name}-${name}")
     endforeach()
 
+    foreach(component ${LLVM_RUNTIME_DISTRIBUTION_COMPONENTS})
+      if(NOT "${target_name}:${target_name}-${component}" IN_LIST extra_targets)
+        list(APPEND ${name}_extra_targets
+          "${target_name}:${target_name}-${component}"
+          "${target_name}:${target_name}-install-${component}")
+      endif()
+    endforeach()
+
     if(LLVM_INCLUDE_TESTS)
       list(APPEND ${name}_test_targets
         "runtimes-test-depends:runtimes-test-depends-${name}"
         "check-runtimes:check-runtimes-${name}")
       foreach(target_name IN LISTS SUB_CHECK_TARGETS)
         list(APPEND ${name}_test_targets "${target_name}:${target_name}-${name}")
         list(APPEND test_targets "${target_name}-${name}")
       endforeach()
else()
         add_custom_target(runtimes-configure)
         add_custom_target(install-runtimes)
         add_custom_target(install-runtimes-stripped)
         if(LLVM_INCLUDE_TESTS)
           add_custom_target(check-runtimes)
           add_custom_target(runtimes-test-depends)
           set(test_targets "")
         endif()
+        if(LLVM_RUNTIME_DISTRIBUTION_COMPONENTS)
+          foreach(component ${LLVM_RUNTIME_DISTRIBUTION_COMPONENTS})
+            add_custom_target(${component})
+            add_custom_target(install-${component})
+          endforeach()
+        endif()
       endif()
 
       foreach(name ${LLVM_RUNTIME_TARGETS})
         set(target ${name})
         string(REPLACE ":" ";" target_list ${target})
         list(GET target_list 0 name)
         list(LENGTH target_list target_list_len)
         if(${target_list_len} GREATER 1)