docs: note that node-gyp@7 should solve Catalina CLT issues

PR-URL: #2156
Reviewed-By: Christian Clauss <cclauss@me.com>

macOS_Catalina.md

@@ -8,6 +8,21 @@ _This document specifically refers to upgrades from previous versions of macOS t
 gyp: No Xcode or CLT version detected!
 ```
 
+## node-gyp v7
+
+The newest release of `node-gyp` should solve this problem. If you are using `node-gyp` directly then you should be able to install v7 and use it as-is.
+
+If you need to use `node-gyp` from within `npm` (e.g. through `npm install`), you will have to install `node-gyp` (either globally with `-g` or to a predictable location) and tell `npm` where the new version is. Either use:
+
+* `npm config set node_gyp <path to node-gyp>`; or
+* run `npm` with an environment variable prefix: `npm_config_node_gyp=<path to node-gyp> npm install`
+
+Where "path to node-gyp" is to the `node-gyp` executable which may be a symlink in your global bin directory (e.g. `/usr/local/bin/node-gyp`), or a path to the `node-gyp` installation directory and the `bin/node-gyp.js` file within it (e.g. `/usr/local/lib/node_modules/node-gyp/bin/node-gyp.js`).
+
+**If you use `npm config set` to change your global `node_gyp` you are responsible for keeping it up to date and can't rely on `npm` to give you a newer version when available.** Use `npm config delete node_gyp` to unset this configuration option.
+
+## Fixing Catalina for older versions of `node-gyp`
+
 ### Is my Mac running macOS Catalina?
 Let's first make sure that your Mac is running Catalina:
 ```
@@ -30,7 +45,7 @@ If test succeeded, _you are done_! You should be ready to install `node-gyp`.
 If test failed, there is a problem with your Xcode Command Line Tools installation. [Continue to Solutions](#Solutions).
 
 ### Solutions
-There are three ways to install the Xcode libraries `node-gyp` needs on macOS. People running Catalina have had success with some but not others in a way that has been unpredictable. 
+There are three ways to install the Xcode libraries `node-gyp` needs on macOS. People running Catalina have had success with some but not others in a way that has been unpredictable.
 
 1. With the full Xcode (~7.6 GB download) from the `App Store` app.
 2. With the _much_ smaller Xcode Command Line Tools via `xcode-select --install`