[CMake] Add test-depends target to build dependencies of check-all

This is just another convenience target for bots to use. It enables isolation of building and testing.

llvm-svn: 262494

llvm/CMakeLists.txt

@@ -727,6 +727,7 @@ if( LLVM_INCLUDE_TESTS )
     DEPENDS ${LLVM_LIT_DEPENDS}
     ARGS ${LLVM_LIT_EXTRA_ARGS}
     )
+  add_custom_target(test-depends DEPENDS ${LLVM_LIT_DEPENDS})
 endif()
 
 if (LLVM_INCLUDE_DOCS)