Correct export.sh failure exit code and cleanup

In failure cases, when idf_export_main() returns 1 (failure),
the export.sh script returns 0 (success). This makes it very
difficult to detect failure when writing scripts that use
export.sh. Furthermore, idf_export_main() does not clean up all
internal variables and functions in failure cases.

Move all cleanup steps into a cleanup function and pass
the return value from idf_export_main() to the cleanup
function so it can return with that same return value.

Signed-off-by: Marek Fiala <marek.fiala@espressif.com>

Closes https://github.com/espressif/esp-idf/pull/5744

export.sh

@@ -126,7 +126,15 @@ __main() {
         __verbose "  ${PATH}"
     fi
 
-    # Clean up
+
+    __verbose "Done! You can now compile ESP-IDF projects."
+    __verbose "Go to the project directory and run:"
+    __verbose ""
+    __verbose "  idf.py build"
+    __verbose ""
+}
+
+__cleanup() {
     unset old_path
     unset paths
     unset path_prefix
@@ -135,16 +143,19 @@ __main() {
     unset idf_exports
     unset ESP_PYTHON
 
+    unset __realpath
+    unset __main
+    unset __verbose
+    unset __enable_autocomplete
+    unset __cleanup
+
     # Not unsetting IDF_PYTHON_ENV_PATH, it can be used by IDF build system
     # to check whether we are using a private Python environment
 
-    __verbose "Done! You can now compile ESP-IDF projects."
-    __verbose "Go to the project directory and run:"
-    __verbose ""
-    __verbose "  idf.py build"
-    __verbose ""
+    return $1
 }
 
+
 __enable_autocomplete() {
     click_version="$(python -c 'import click; print(click.__version__.split(".")[0])')"
     if [[ click_version -lt 8 ]]
@@ -171,8 +182,4 @@ __enable_autocomplete() {
 
 __main
 __enable_autocomplete
-
-unset __realpath
-unset __main
-unset __verbose
-unset __enable_autocomplete
+__cleanup $?