Tools: Auto-detect IDF_PATH in export.fish, fix setting environmental variables

Edited GitHub user's change to keep the echo message consistent with other export scripts
Fixed working with environmental variables in fish.

pull request sha: 5a646b806722da5e4743f3808bfca18d17ba299d

export.fish

@@ -7,8 +7,8 @@ end
 
 function __main
     if not set -q IDF_PATH
-        set -x IDF_PATH (cd (dirname (status -f)); and pwd)
-        echo "Chosen IDF_PATH: $IDF_PATH"
+        set -gx IDF_PATH (cd (dirname (status -f)); and pwd)
+        echo "Setting IDF_PATH to '$IDF_PATH'"
     end
 
     set script_dir (cd (dirname (status -f)); and pwd)
@@ -36,8 +36,8 @@ function __main
 
     echo "Adding ESP-IDF tools to PATH..."
     # Call idf_tools.py to export tool paths
-    set -x IDF_TOOLS_EXPORT_CMD "$IDF_PATH"/export.fish
-    set -x IDF_TOOLS_INSTALL_CMD "$IDF_PATH"/install.fish
+    set -gx IDF_TOOLS_EXPORT_CMD "$IDF_PATH"/export.fish
+    set -gx IDF_TOOLS_INSTALL_CMD "$IDF_PATH"/install.fish
     # Allow calling some IDF python tools without specifying the full path
     # "$IDF_PATH"/tools is already added by 'idf_tools.py export'
     set IDF_ADD_PATHS_EXTRAS "$IDF_PATH"/components/esptool_py/esptool