RFR[8u-dev]: 8139040: Fix initializations before ShouldNotReachHere() etc. and enable -Wuninitialized on linux.

[Cheleswer Sahu]

Could somebody please review the below backport changes.

Hi,

Please review the code changes for backport "https://bugs.openjdk.java.net/browse/JDK-8139040".

JBS link: https://bugs.openjdk.java.net/browse/JDK-8139040
JDK9 changeset: 
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/825cee2cd7a6
JDK9 review thread: 
http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2015-October/016005.html

JDK8u webrev: http://cr.openjdk.java.net/~csahu/8139040/

List of files not included in this backport:
    src/share/vm/classfile/compactHashtable.cpp
    src/share/vm/opto/compile.hpp
    src/share/vm/opto/superword.cpp
    src/share/vm/runtime/arguments.cpp
    Reason: Above file are either not available in JDK8u or changes are not applicable.

make/linux/makefiles/gcc.make
   Reason: This file contain changes related  "-Wuninitialized" flag which is available since gcc4.8 . JDK8u is supporting lower version of gcc, hence not included this fix.


Regards,
Cheleswer