Transition the JDK to the common standard of C11

At the time of writing, the JDK does not have a common standard across the codebase. C99 is loosely aimed for on every compiler except for Visual C++, which only supports C90 at best. As noted in one section of the build system, having all sources at the same standard is ideal, but deemed too difficult to achieve. With newer versions of Visual C++ having flags that now support C11, and JDK-8288293 suffering slightly from compiler specific roadblocks however, an attempt is underway to move all of the JDK's C sources to C11, not only for the guarantee that all sources will conform to the same standard, but also to gain access to numerous useful features that C11 offers, which will likely benefit the JDK as a whole, as well as reduce the amount of compiler specific extensions and ugly workarounds required in areas of the JDK written in C.