…ilds (x86) (#4)

* Support NPM versions that don't export config environment variables

The automatic exportation of environment variables based on the config key
in package.json was removed in later versions of Node.js. Here, we
manually set the environment variable if it's not automatically set.

* Install ninja dep

Ninja is a prerequisite for the build. On Ubuntu install it with apt-get,
and on GitHub's macOS Docker image it needs to come from Homebrew.

* Remove support for external startup data

This makes V8 always build with v8_use_external_startup_data=false.
Since that was previously controlled by the EXTERNAL_STARTUP_DATA
variable, we can remove that variable. If we're not using external startup
heap snapshots, we also don't need to export mksnapshot and mkcodecache;
they are now only used internally by the V8 build. This also makes a
TOOLS_ONLY build and therefore a tools_macos_android build obsolete.

Summary:
- Remove EXTERNAL_STARTUP_DATA
- Remove TOOLS_ONLY
- Remove MKSNAPSHOT_ONLY
- Remove MKCODECACHE_ONLY
- Remove patch to allow monolithic build with external startup data
- Remove patch to export mkcodecache
- Remove tools_macos_android workflow