Warn user when auto-detection returns 'generic'.

Details:
- Added logic to configure that causes the script to output a warning
  to the user if/when "./configure auto" is run and the underlying
  hardware feature detection code is unable to identify the hardware.
  In these cases, the auto-detect code will return 'generic', which
  is likely not what the user expected, and a flag will be set so that
  a message is printed at the end of the configure output. (Thankfully,
  we don't expect this scenario to play out very often.) Thanks to
  Devin Matthews for suggesting this fix #384.

configure

@@ -2430,8 +2430,22 @@ main()
 		# Call the auto_detect() function and save the returned string in
 		# config_name.
 		config_name=$(auto_detect)
+		#config_name="generic"
 
 		echo "${script_name}: hardware detection driver returned '${config_name}'."
+
+		# If the auto-detect code returned the "generic" string, it means we
+		# were unable to automatically detect the user's hardware type. While
+		# this is going to be a rare event, it will likely lead the user to
+		# experience much lower performance than expected, and thus we will
+		# warn them about it at the end of the configure output (to increase
+		# the chances that they see it).
+		if [ "${config_name}" = "generic" ]; then
+
+			warn_user_generic=1
+		else
+			warn_user_generic=0
+		fi
 	else
 
 		# Use the command line argument as the configuration name.
@@ -3485,6 +3499,18 @@ main()
 		echo "${script_name}: configured to build within top-level directory of source distribution."
 	fi
 
+	if [ "${warn_user_generic}" = "1" ]; then
+
+		echo "${script_name}: "
+		echo "${script_name}: *** Unable to automatically detect hardware type! ***"
+		echo "${script_name}: "
+		echo "${script_name}: NOTE: configure was unable to identify a subconfiguration"
+		echo "${script_name}: optimized for your hardware. As a result, the 'generic'"
+		echo "${script_name}: subconfiguration (with low-performance reference kernels)"
+		echo "${script_name}: will be used. For support, please open an issue on GitHub"
+		echo "${script_name}: at https://github.com/flame/blis/issues."
+		echo "${script_name}: "
+	fi
 
 	# Exit peacefully.
 	return 0