RFR: JDK-8200738 Use --hash-style=gnu for gcc

Fri Jun 12 15:42:42 UTC 2020

When support for gnu hash tables were added to the gcc toolchains, the 
OpenJDK build system added a hack to change --hash-style=gnu to 
--hash-style=both unconditionally, citing compatibility concerns.

--hash-style=gnu has a very slight performance advantage over 
--hash-style=both (very small static footprint reductions, tiny startup 
cost differences). Both --hash-style=gnu and --hash-style=both have a 
small to potentially large performance advantage over --hash-style=sysv

We should only use --hash-style=gnu. It's been the default in Ubuntu's 
build of gcc since gcc 4.4[1], and likely similar in other distros.

I also removed LIBJSIG_NOEXECSTACK_LDFLAGS which is no longer used.

Bug: https://bugs.openjdk.java.net/browse/JDK-8200738
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8200738-use-hash-style-gnu/webrev.01

/Magnus

[1] https://launchpad.net/ubuntu/maverick/+source/gcc-4.4/+changelog