Add macOS (and Linux) build support

[Copilot]

• Fix premake5.lua: move architecture 'x86' to Windows-only filter
• Fix premake5.lua: add macOS/Linux platform defines (PLATFORM_MACOS, PLATFORM_LINUX)
• Fix premake5.lua: use platform-specific Lua executable name
• Add init.sh shell script for macOS/Linux users
• Add GitHub Actions workflow for macOS build
• Fix src/os_chdir.c: add #include <unistd.h> for chdir() on macOS/Linux
• Fix src/objediting.cpp: change constexpr char* to constexpr const char* for string literals
• Add *.o to .gitignore to prevent build artifacts from being committed
• Fix premake5.lua: move Maps linker flag to Windows-only filter (Apple ld does not support -Map=)
• Fix bin/build.lua: create output directory before writing generated .lua.cpp/.lua.h files (.build/lua/ didn't exist on macOS/Linux)

[dulingzhi]

@copilot compile error

[Copilot]

@copilot compile error

Fixed in ffac8f5. Two compile errors were addressed:

1. src/os_chdir.c: Added #include <unistd.h> in the non-Windows branch — chdir() requires this header on macOS/Linux; without it, modern compilers (Clang and GCC ≥14) error on the implicit function declaration.

2. src/objediting.cpp: Changed constexpr char* → constexpr const char* for the three string literal constants — assigning string literals (type const char[]) to char* is ill-formed in C++11 and is an error in Clang.

[dulingzhi]

@copilot compile error

[Copilot]

@copilot compile error

Fixed in 743c2b7. The macOS build was failing with ld: unknown options: -Map=bin/Release/Lua.map because Apple's linker doesn't support the -Map option (a GNU ld feature). The 'Maps' premake flag that generates it has been moved from the workspace-level flags {} into the filter 'system:Windows' block so it only applies on Windows.

[dulingzhi]

@copilot fix macOS build failed

[Copilot]

@copilot fix macOS build failed

Fixed in 205d9fe. The macOS build was failing because bin/build.lua tried to write generated files to .build/lua/ before that directory existed — on macOS/Linux the gmake build system doesn't auto-create intermediate output directories the way Windows does. Added mkdir -p (or the Windows equivalent) at the start of main() before the first writeFile call.