Support ARM Compiler for Embedded on STM32U5

[mattia-moffa]

This adds support for the ARM Compiler for Embedded suite (i.e. armclang, armlink, armar, fromelf) beside GNU and LLVM. Only stm32u5 with TZEN=1 is supported for now (more targets would require writing scatter files for them).

Also adds a DEBUG_UART driver for the stm32u5.

[Copilot]

Pull request overview

Adds build support for the ARM Compiler for Embedded (AC6: armclang/armlink/armar/fromelf) alongside existing GNU/LLVM flows, currently scoped to STM32U5 with TrustZone enabled (TZEN=1). Also introduces a DEBUG UART backend for STM32U5 and updates memory/linker configuration accordingly.

Changes:

• Introduces an ARM toolchain mode (USE_ARMCLANG=1) with armlink scatter-file linking, symbol mapping, and a fromelf-backed objcopy adapter.
• Adds STM32U5-specific scatter files for both wolfBoot (secure) and test-app (non-secure), plus updates STM32U5 memory layout config.
• Adds a STM32U5 UART driver and wires it into DEBUG UART initialization paths and build rules.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tools/armclang/objcopy.sh	Adds a small objcopy-compatible wrapper around fromelf for bin/hex/srec output generation.
tools/armclang/armclang_stubs.c	Provides ARMCLANG-specific stubs (dead refs + heap allocator) for TZ/PKCS11 configurations.
test-app/wcs/user_settings.h	Adjusts clock_gettime forward declarations for the test-app wolfCrypt settings.
test-app/Makefile	Adds ARMCLANG link flow for test-app and conditionally builds STM32U5 non-secure UART driver for DEBUG UART.
test-app/ARM-stm32u5-ns.sct	New armlink scatter file for STM32U5 non-secure test-app image (TZEN=1).
options.mk	Adds USE_ARMCLANG option and enforces mutual exclusivity with GCC/clang modes and ARMORED.
Makefile	Adds ARMCLANG link flow for wolfBoot (scatter linking + symbol mapping) and updates clean targets for UART objects.
hal/uart/uart_drv_stm32u5.c	New STM32U5 UART backend (USART1 on PA9/PA10) with optional uart_write() for DEBUG UART.
hal/stm32u5.sct	New armlink scatter file for STM32U5 wolfBoot secure image (TZEN=1).
hal/stm32u5.ld	Fixes FLASH region length expression to be based on @WOLFBOOT_ORIGIN@.
hal/stm32u5.h	Adds STM32U5 UART register/pin definitions and secure vs non-secure base selection.
hal/stm32u5.c	Exposes flash helper functions via hal_flash_* names and adds DEBUG UART init + TZ unsecure config for USART1/GPIOA.
docs/compile.md	Documents how to build wolfBoot with ARM Compiler for Embedded (USE_ARMCLANG=1).
config/examples/stm32u5-wolfcrypt-tz.config	Updates STM32U5 TZ wolfcrypt example addresses (keyvault/NSC/partitions).
arch.mk	Adds ARMCLANG toolchain wiring (CC/LD/AR/FROMELF/OBJCOPY, armlink flags, scatter symbol mapping).
.gitignore	Ignores generated config/*.sct scatter outputs.

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