HookSystem: rename PAGESIZE_VAR from PAGESIZE to avoid conflict

[earboxer]

Describe your PR, what does it fix/add?

This fixes a build issue with v0.34.0 (on alpine linux, and maybe others?)

In file included from /usr/include/limits.h:40,
                 from /usr/include/fortify/wchar.h:23,
                 from /usr/include/c++/13.2.1/cwchar:44,
                 from /usr/include/c++/13.2.1/bits/postypes.h:40,
                 from /usr/include/c++/13.2.1/iosfwd:42,
                 from /usr/include/c++/13.2.1/ios:40,
                 from /usr/include/c++/13.2.1/ostream:40,
                 from /usr/include/c++/13.2.1/bits/unique_ptr.h:42,
                 from /usr/include/c++/13.2.1/memory:78,
                 from ../src/Compositor.hpp:3,
                 from ../src/pch/pch.hpp:1:
../src/plugins/HookSystem.cpp: In member function 'bool CFunctionHook::hook()':
../src/plugins/HookSystem.cpp:193:20: error: expected unqualified-id before numeric constant
  193 |     const auto     PAGESIZE  = sysconf(_SC_PAGE_SIZE);
      |                    ^~~~~~~~
ninja: subcommand failed
>>> ERROR: hyprland: build failed

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

Is it ready for merging, or does it need work?

Yes, it is ready for merging

[vaxerski]

lgtm

[vaxerski]

needs a clang-format