Sanity check of Hermes source directory via environment variable, when building Android projects

[kraenhansen]

I've investigated ways of letting the host package drive building Hermes from (our) source. So far, I haven't found any.

In the absence of a fully automated solution, it would be good if we exist early with instructions on how to set the REACT_NATIVE_OVERRIDE_HERMES_DIR environment variable if missing:

export REACT_NATIVE_OVERRIDE_HERMES_DIR=`npx react-native-node-api vendor-hermes --silent`

I would expect the error to be thrown from a new task around here:

react-native-node-api/packages/host/android/build.gradle

Lines 141 to 157 in 8dac805

	// Custom task to fetch jniLibs paths via CLI
	task linkNodeApiModules {
	doLast {
	exec {
	// TODO: Support --strip-path-suffix
	commandLine 'npx', 'react-native-node-api', 'link', '--android', rootProject.rootDir.absolutePath
	standardOutput = System.out
	errorOutput = System.err
	// Enable color output
	environment "FORCE_COLOR", "1"
	}
	android.sourceSets.main.jniLibs.srcDirs += file("../auto-linked/android").listFiles()
	}
	}
	preBuild.dependsOn linkNodeApiModules