Add LLVM/Clang toolchain support with auto-detection

Add automatic detection and configuration for LLVM/Clang toolchain
alongside existing GCC support. The build system now detects which
compiler is available and configures appropriate flags and tools.

- Auto-detect LLVM/Clang via CC_IS_CLANG variable
- Add Clang-specific flags (--target, warning suppressions)
- Use LLVM binutils (ld.lld, llvm-objdump, etc.) when Clang detected
- Refactor to use common ARCH_FLAGS for consistency
- Maintain backward compatibility with GCC toolchain

Author: G36maid

arch/riscv/build.mk

@@ -17,27 +17,51 @@ DEFINES := -DF_CPU=$(F_CLK) \
            -DF_TIMER=$(F_TICK) \
            -include config.h
 
-ASFLAGS = -march=rv32imzicsr -mabi=ilp32
-CFLAGS += -Wall -Wextra -Wshadow -Wno-unused-parameter -Werror
+CROSS_COMPILE ?= riscv-none-elf-
+
+# Detect LLVM/Clang toolchain (allow user override)
+CC_IS_CLANG ?= $(shell $(CROSS_COMPILE)clang --version 2>/dev/null | grep -qi clang && echo 1)
+
+# Architecture flags
+ARCH_FLAGS = -march=rv32imzicsr -mabi=ilp32
+
+# Common compiler flags
+CFLAGS += -Wall -Wextra -Werror -Wshadow -Wno-unused-parameter
 CFLAGS += -O2 -std=gnu99
-CFLAGS += -march=rv32imzicsr -mabi=ilp32
+CFLAGS += $(ARCH_FLAGS)
 CFLAGS += -mstrict-align -ffreestanding -nostdlib -fomit-frame-pointer
 CFLAGS += $(INC_DIRS) $(DEFINES) -fdata-sections -ffunction-sections
-ARFLAGS = r
 
-# Linker flags
-LDFLAGS = -melf32lriscv --gc-sections
-LDSCRIPT = $(ARCH_DIR)/riscv32-qemu.ld
+ifeq ($(CC_IS_CLANG),1)
+    CC    = $(CROSS_COMPILE)clang
+    AS    = $(CROSS_COMPILE)clang
+    LD    = $(CROSS_COMPILE)ld.lld
+    DUMP  = $(CROSS_COMPILE)llvm-objdump -M no-aliases
+    READ  = $(CROSS_COMPILE)llvm-readelf
+    OBJ   = $(CROSS_COMPILE)llvm-objcopy
+    SIZE  = $(CROSS_COMPILE)llvm-size
 
-CROSS_COMPILE ?= riscv-none-elf-
-CC = $(CROSS_COMPILE)gcc
-AS = $(CROSS_COMPILE)as
-LD = $(CROSS_COMPILE)ld
-DUMP = $(CROSS_COMPILE)objdump -Mno-aliases
-READ = $(CROSS_COMPILE)readelf
-OBJ = $(CROSS_COMPILE)objcopy
-SIZE = $(CROSS_COMPILE)size
-AR = $(CROSS_COMPILE)ar
+    CFLAGS += --target=riscv32-unknown-elf
+    CFLAGS += -Wno-unused-command-line-argument
+    ASFLAGS = --target=riscv32-unknown-elf
+    LDFLAGS = -m elf32lriscv
+else
+    CC    = $(CROSS_COMPILE)gcc
+    AS    = $(CROSS_COMPILE)as
+    LD    = $(CROSS_COMPILE)ld
+    DUMP  = $(CROSS_COMPILE)objdump -Mno-aliases
+    READ  = $(CROSS_COMPILE)readelf
+    OBJ   = $(CROSS_COMPILE)objcopy
+    SIZE  = $(CROSS_COMPILE)size
+    LDFLAGS = -melf32lriscv
+endif
+
+AR    	= $(CROSS_COMPILE)ar
+ASFLAGS += $(ARCH_FLAGS)
+LDFLAGS += --gc-sections
+
+ARFLAGS = r
+LDSCRIPT = $(ARCH_DIR)/riscv32-qemu.ld
 
 HAL_OBJS := boot.o hal.o muldiv.o
 HAL_OBJS := $(addprefix $(BUILD_KERNEL_DIR)/,$(HAL_OBJS))