RFR: Remove sys/ prefix from poll.h/signal.h includes

[Mikael Vidstedt]

In several places in the JDK sources poll.h and signal.h are included through sys/{poll.h,signal.h}. The posix spec says the files should be included without the sys/ prefix, and musl issues a warning when sys/{poll.h,signal.h} are included.

This change simple removes the sys/ prefix in all the relevant places. I’ve tried my best to verify that this works on all the platforms/toolchains I have access to, and also got help from the SAP guys to verify that it should work on AIX as well.

hotspot: http://cr.openjdk.java.net/~mikael/webrevs/portola/pollsignal/webrev.00/hotspot/webrev/
jdk: http://cr.openjdk.java.net/~mikael/webrevs/portola/pollsignal/webrev.00/jdk/webrev/

Cheers,
Mikael