Check include/mbedtls exists before including from it

Signed-off-by: Felix Conway <felix.conway@arm.com>
diff --git a/programs/test/generate_cpp_dummy_build.sh b/programs/test/generate_cpp_dummy_build.sh
index 05bdd34..7b4f520 100755
--- a/programs/test/generate_cpp_dummy_build.sh
+++ b/programs/test/generate_cpp_dummy_build.sh
@@ -52,9 +52,11 @@
         esac
     done
 
-    for header in tf-psa-crypto/include/mbedtls/*.h; do
-        echo "#include \"${header#tf-psa-crypto/include/}\""
-    done
+    if [ -d "tf-psa-crypto/include/mbedtls" ]; then
+        for header in tf-psa-crypto/include/mbedtls/*.h; do
+            echo "#include \"${header#tf-psa-crypto/include/}\""
+        done
+    fi
 
     for header in tf-psa-crypto/include/psa/*.h; do
         case ${header#tf-psa-crypto/include/} in