Support Building on macOS

[LiruMouse]

Description

Added support for building on macOS.

The macOS version of ARM's toolchain appears to be using a different version of newlib, which may account for the slightly larger sized binary than what Arch is producing.

Changes Made:

• build.sh: Support using sysctl to get the cpu count
• Makefile & setup_macos.sh: Gather dependencies from brew for Mac
• cmake/gcc-arm-none-eabi.cmake:
  • Allow setting TOOLCHAIN_PREFIX for all platforms
  • When TOOLCHAIN_PREFIX is unset on macos, try where brew puts it by default
• documentation/mbt.md & README: Document build
  • README: Split platform Build Steps via markdown headings

Type of Change

• New feature (non-breaking change which adds functionality)
• Documentation update

Testing Environment

• IDE: N/A (command-line build)
• Version: N/A
• Compiler Hardware: M4 Max running 15.7.2
• Compiler: arm-none-eabi-gcc (GCC) 15.2.0
  • Also built/tested with 14.2, but that made the setup overly complicated since brew's cask uses 15.2 now.
• Debugger: N/A

How Has This Been Tested?

• Build completes successfully with make
• ELF file validated as ARMv8-M architecture
• Binary/HEX files generated in artifacts directory
• Memory usage within device limits (RAM: 26.88%, FLASH: 44.72%)
• Moved the artifacts onto an SD card and went through
  • Settings->Firmware update->Image File
  • Selected the correct image from the SD card
  • Checked that the versions displayed looked correct
  • Selected Firmware update and watched until it said the update was successful
  • Checked out that my M1 wasn't bricked.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings