RFR: JDK-8164402 key word 'requires' appearing in comment causing a build failure

[Tim Bell]

Hello

Earlier today a javadoc change surprised us by causing JDK 9 builds to 
fail on all platforms, due to a modules 'requires' statement error.

The fix is to have make/common/Modules.gmk be more selective when 
processing 'requires', so that comment lines are filtered out.

Here is the bug report:
https://bugs.openjdk.java.net/browse/JDK-8164402

And the webrev:
http://cr.openjdk.java.net/~tbell/8164402/webrev/

Thanks in advance-

Tim