Add FATFS build test workflow #220

Job	Run time
Build wolfssl (ubuntu-latest)	2s
Build wolfssl (macos-latest)	6s
Build wolfssh (ubuntu-latest)	16s
Build wolfssh (ubuntu-latest, --enable-all)	19s
Build wolfssh (ubuntu-latest, --enable-sftp)	16s
Build wolfssh (ubuntu-latest, --enable-scp)	22s
Build wolfssh (ubuntu-latest, --enable-shell)	17s
Build wolfssh (macos-latest)	40s
Build wolfssh (macos-latest, --enable-all)	45s
Build wolfssh (macos-latest, --enable-sftp)	33s
Build wolfssh (macos-latest, --enable-scp)	50s
Build wolfssh (macos-latest, --enable-shell)	35s
	5m 1s

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