Please review this change which disables warnings for left shift of a negative value when compiling HotSpot with gcc or clang. This warning isn't helpful, given that all compilers seem to do the obvious thing, and that obvious thing will soon-ish (C++20) be the specified thing. See the CR for more details.
CR: https://bugs.openjdk.java.net/browse/JDK-8240259 Webrev: https://cr.openjdk.java.net/~kbarrett/8240259/open.00/ Testing: mach5 tier1. Also tier1-5 with C++14 enabled. Note that there are already occurrences of left shift of negative values in our code, with no apparent consequences, even when testing with C++11/14 enabled.
