Fix build when LLVM_BUILTIN_TARGETS is not set

[kongyi]

Summary

If LLVM_BUILTIN_TARGETS is not set, no OS specific variants will be created, causing CMake build failure. Depend on the generic builtins target if LLVM_BUILTIN_TARGETS is not set.

[smeenai]

Ah, I didn't consider the case where you were using LLVM_RUNTIME_TARGETS but not LLVM_BUILTIN_TARGETS. Thanks.

[phosek]

LGTM

llvm/runtimes/CMakeLists.txt

else()
           add_custom_target(install-${component})
           add_custom_target(install-${component}-stripped)
         endforeach()
       endif()
     endif()
 
     foreach(name ${LLVM_RUNTIME_TARGETS})
       if(builtins_dep)
+        if (LLVM_BUILTIN_TARGETS)
           set(builtins_dep_name "${builtins_dep}-${name}")
+        else()
+          set(builtins_dep_name ${builtins_dep})
+        endif()
       endif()
       runtime_register_target(${name} ${name}
         DEPENDS ${builtins_dep_name})
 
       add_dependencies(runtimes runtimes-${name})
       add_dependencies(runtimes-configure runtimes-${name}-configure)
       add_dependencies(install-runtimes install-runtimes-${name})
       add_dependencies(install-runtimes-stripped install-runtimes-${name}-stripped)