The file API code used unsigned long to hold the major version in most
places, but not all. Some places used unsigned int, and an important one
of those is the cmFileApi::BuildVersion() function. As a result, it has never
been safe for a large value not representable by an unsigned int to be
used in these variables.
Convert all of the file API version number variables and function arguments
to use unsigned int consistently. This avoids any size mismatch warnings
when passing values around. They also don't need to be unsigned long,
as we never expect version numbers to be anything even close to what
an unsigned int cannot represent.
#pragma once is a widely supported compiler pragma, even though it is
not part of the C++ standard. Many of the issues keeping #pragma once
from being standardized (distributed filesystems, build farms, hard
links, etc.) do not apply to CMake - it is easy to build CMake on a
single machine. CMake also does not install any header files which can
be consumed by other projects (though cmCPluginAPI.h has been
deliberately omitted from this conversion in case anyone is still using
it.) Finally, #pragma once has been required to build CMake since at
least August 2017 (7f29bbe6 enabled server mode unconditionally, which
had been using #pragma once since September 2016 (b13d3e0d)). The fact
that we now require C++11 filters out old compilers, and it is unlikely
that there is a compiler which supports C++11 but does not support
#pragma once.
