RFR [XS] jdk11 - 8234809: set relro in linker flags when building with gcc

[Baesken, Matthias]

Hello,  please review  the jdk11 downport of  8234809 .

The patch form jdk/jdk  did not apply  directly   so  make/autoconf/flags-ldflags.m4   had to be adjusted a little bit for jdk11 .

Original discussion :

https://mail.openjdk.java.net/pipermail/build-dev/2019-November/026347.html

+

https://mail.openjdk.java.net/pipermail/build-dev/2019-November/026365.html



Bug/ jdk11 webrev :

https://bugs.openjdk.java.net/browse/JDK-8234809

http://cr.openjdk.java.net/~mbaesken/webrevs/8234809_jdk11.0/

Thanks, Matthias