Fix DEX_ONLY compile error in cpu_external_function.cpp

Move definition of StaticInitializers out of `#ifndef NGRAPH_DEX_ONLY`

src/ngraph/runtime/cpu/cpu_external_function.cpp

@@ -198,16 +198,16 @@ runtime::cpu::CPU_ExternalFunction::~CPU_ExternalFunction()
 {
 }
 
-#if !defined(NGRAPH_DEX_ONLY)
-
-static const string s_output_dir = "cpu_codegen";
-
 class StaticInitializers
 {
 public:
     StaticInitializers(string directory) { ngraph::file_util::remove_directory(directory); }
 };
 
+#if !defined(NGRAPH_DEX_ONLY)
+
+static const string s_output_dir = "cpu_codegen";
+
 static string emit_string_array(const vector<string>& s, size_t max_line_length)
 {
     stringstream ss;