RFR: JDK-8201508: Macosx builds fail in GenerateLinkOptData.gmk

[Magnus Ihse Bursie]

Looks good to me. Thanks for fixing this. I didn't think there was anything platform dependent in my fix, so I only tested it locally. :( 

/Magnus

> 12 apr. 2018 kl. 23:28 skrev Erik Joelsson <erik.joelsson at oracle.com>:
> 
> All macosx builds in CI currently fail. This is caused by in issue with JDK-8201483 which leaves the JVM_VARIANTS_server variable empty. The construct used to subtract one set of strings from another doesn't work quite as expected with bsd grep.
> 
> result=`$GREP -Fvx "$legal_values" <<< "$values_to_check" | $GREP -v '^$'`
> 
> If the set to subtract ($legal_values) is empty, gnu grep returns all values (as expected) while bsd grep returns nothing. To fix this I've added an explicit check for the base case of legal_values being empty. This seems to make --with-jvm-features work correctly on macosx and still work correctly on Linux. A verification distributed build is under way.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8201508
> 
> Webrev: http://cr.openjdk.java.net/~erikj/8201508/webrev.01/
> 
> /Erik
>