[Executorch][llama] Split main in lib + binary

Main reason to do so is to allow internal benchmarking binary to link against main_lib

Differential Revision: [D87547090](https://our.internmc.facebook.com/intern/diff/D87547090/)

ghstack-source-id: 324690959
Pull Request resolved: #15919

Author: kimishpatel

examples/models/llama/main.cpp

@@ -64,6 +64,8 @@ DEFINE_int32(
 
 DEFINE_bool(warmup, false, "Whether to run a warmup run.");
 
+std::vector<std::string> parseStringList(const std::string& input);
+
 // Helper function to parse comma-separated string lists
 std::vector<std::string> parseStringList(const std::string& input) {
   std::vector<std::string> result;

examples/models/llama/targets.bzl

@@ -5,8 +5,8 @@ def define_common_targets():
         if not runtime.is_oss or not aten:
             aten_suffix = "_aten" if aten else ""
 
-            runtime.cxx_binary(
-                name = "main" + aten_suffix,
+            runtime.cxx_library(
+                name = "main" + aten_suffix + "_lib",
                 srcs = [
                     "main.cpp",
                 ],
@@ -25,3 +25,11 @@ def define_common_targets():
                 ],
                 **get_oss_build_kwargs()
             )
+
+            runtime.cxx_binary(
+                name = "main" + aten_suffix,
+                srcs = [],
+                deps = [
+                    ":main" + aten_suffix + "_lib",
+                ],
+            )