[Fuchsia] Add LLDB to CLANG_BOOTSTRAP_TARGETS.

[mysterymath]

Summary

stage2-check-lldb should be run in a 2-stage build to test the final
LLDB artifact, so it and related targets must be exported to the stage 1
project.

[phosek]

LGTM

clang/cmake/caches/Fuchsia.cmake

if(STAGE2_LINUX_${target}_SYSROOT)
     set(RUNTIMES_${target}_SANITIZER_CXX_ABI "libc++" CACHE STRING "")
     set(RUNTIMES_${target}_SANITIZER_CXX_ABI_INTREE ON CACHE BOOL "")
   endif()
 endif()
 
 set(BOOTSTRAP_LLVM_ENABLE_LLD ON CACHE BOOL "")
 set(BOOTSTRAP_LLVM_ENABLE_LTO ON CACHE BOOL "")
 
-set(CLANG_BOOTSTRAP_TARGETS
+set(_FUCHSIA_BOOTSTRAP_TARGETS
   check-all
   check-clang
   check-lld
   check-llvm
   check-polly
   llvm-config
   clang-test-depends
   lld-test-depends
   llvm-test-depends
   test-suite
   test-depends
   distribution
   install-distribution
   install-distribution-stripped
   install-distribution-toolchain
-  clang CACHE STRING "")
+  clang)
 
 set(FUCHSIA_ENABLE_LLDB OFF CACHE BOOL "Enable LLDB")
 if(FUCHSIA_ENABLE_LLDB)
   list(APPEND _FUCHSIA_ENABLE_PROJECTS lldb)
+  list(APPEND _FUCHSIA_BOOTSTRAP_TARGETS check-lldb lldb-test-depends)
 endif()
 set(LLVM_ENABLE_PROJECTS ${_FUCHSIA_ENABLE_PROJECTS} CACHE STRING "")
+set(CLANG_BOOTSTRAP_TARGETS ${_FUCHSIA_BOOTSTRAP_TARGETS} CACHE STRING "")
 
 get_cmake_property(variableNames VARIABLES)
 foreach(variableName ${variableNames})
   if(variableName MATCHES "^STAGE2_")
     string(REPLACE "STAGE2_" "" new_name ${variableName})
     list(APPEND EXTRA_ARGS "-D${new_name}=${${variableName}}")
   endif()
 endforeach()