RFR: JDK-8171922: Hotspot code coverage doesn't seem to work

[Erik Joelsson]

Hello,

When the new hotspot build was introduced, we missed converting the 
support for compiling in code coverage using gcov. This patch fixes 
that. While making the change I discovered that the LEGACY_EXTRA_*FLAGS 
variables are now unused and can finally be completely removed, so I 
went ahead and did that too.

Bug: https://bugs.openjdk.java.net/browse/JDK-8171922

Webrev: http://cr.openjdk.java.net/~erikj/8171922/webrev.01/

/Erik