sw:vec-iree: Make internal model build optional

So we don't break `m simulate` for external contributors

Change-Id: I29b0b731fe74d3727634da3f7c89866b81dbde38

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6b1c301..e82e6aa 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -13,6 +13,7 @@
 )
 
 set(BUILD_RV64_LINUX OFF CACHE BOOL "Build RISC-V 64-bit Linux target (default: OFF)")
+set(BUILD_INTERNAL_MODELS OFF CACHE BOOL "Build applications from internal models (default: OFF")
 
 #-------------------------------------------------------------------------------
 # Springbok-specific settings

samples/float_model_embedding/CMakeLists.txt

diff --git a/samples/float_model_embedding/CMakeLists.txt b/samples/float_model_embedding/CMakeLists.txt
index 7e64777..f3445e9 100644
--- a/samples/float_model_embedding/CMakeLists.txt
+++ b/samples/float_model_embedding/CMakeLists.txt
@@ -3,6 +3,10 @@
 # and "+experimental-v" are for RVV support.
 #-------------------------------------------------------------------------------
 
+if(NOT ${BUILD_INTERNAL_MODELS})
+  return()
+endif()
+
 if(NOT ${BUILD_WITH_SPRINGBOK})
   springbok_bytecode_module(
     NAME