[CMake] Address the issue introduced in #69869

While extracting the existing functionality into a function, one of the
variable usages wasn't correctly updated.

Author: petrhosek

llvm/runtimes/CMakeLists.txt

@@ -174,7 +174,7 @@ endif()
 function(_get_runtime_name name out_var)
   string(FIND ${name} "lib" idx)
   if(idx EQUAL 0 AND NOT ${name} STREQUAL "libc")
-    string(SUBSTRING ${name} 3 -1 entry)
+    string(SUBSTRING ${name} 3 -1 name)
   endif()
   set(${out_var} ${name} PARENT_SCOPE)
 endfunction()