feat: Add experimental Linux build support

[killerdevildog]

Summary

Add experimental Linux build support for ArcGameEngine. The project now compiles and runs on Linux without modifying any third-party vendor source code.

What Works

• Full project builds successfully on Linux (all vendor libraries, Arc core engine, and Arc-Editor)
• Arc-Editor launches and runs on Linux/X11
• No third-party/vendor source files are modified — all fixes are applied through project-owned build configuration and scripts

Changes

Arc/src/arcpch.h

• Add #include <cstdint> to the precompiled header, ensuring fixed-width integer types (uint32_t, uint64_t, etc.) are available before any vendor headers are included.

Arc/vendor/JoltPhysics/premake5.lua

• Add forceincludes { "cstdint" } under the Linux filter. JoltPhysics compiles as a separate static library with its own translation units, so it does not use Arc's precompiled header. This ensures <cstdint> is implicitly included before each JoltPhysics source file on Linux.

scripts/GenerateMake.sh

• Add a build-time patch that inserts a NULL stub for the missing setWindowTitleBar function pointer in GLFW's x11_init.c. The patch is idempotent (only applies if not already present) and includes a guard to prevent double-application.

  Background: The upstream GLFW fork (MohitSethi99/glfw) has a bug where the X11 platform struct initializer is missing the setWindowTitleBar entry that exists in both win32_init.c and null_init.c. This causes every function pointer after that slot to be assigned to the wrong position, resulting in type mismatch compilation errors. The Wayland init (wl_init.c) has the same issue.

README.md

• Add Linux build section with dependency installation instructions and build commands
• Update platform badge to reflect Windows (Primary) | Linux (Experimental)

Known Limitations / Future Work

These should be addressed in separate PRs:

1. GLFW upstream fix needed — The setWindowTitleBar function pointer is missing from both x11_init.c and wl_init.c in MohitSethi99/glfw. A PR should be submitted to that repo to add the proper function entries. Once merged, the build-time patch in GenerateMake.sh can be removed.

2. Wayland support — The build currently targets X11 only. Wayland has the same missing function pointer issue and is not yet tested.

3. Shader warnings — The editor runs but produces m_Params used uninitialized shader warnings at startup. These are pre-existing and not related to this PR.

4. CI/CD — No Linux CI pipeline exists yet. A GitHub Actions workflow for Linux builds would help catch regressions.

Testing

• OS: Ubuntu/Debian
• Compiler: Clang 18.1.3
• Dependencies: build-essential, clang, libc++-dev, libstdc++-14-dev
• All vendor libraries compile without errors
• Arc core engine library links successfully
• Arc-Editor builds and launches on X11