build: use i686 ELF toolchain on macOS

Homebrew doesn't provide an i386 ELF toolchain as an official formula,
though one is available from the tap `nativeos/i386-elf-toolchain`.
Unfortunately, the binaries included in this toolchain conflicts with
the deprecated names for the official x86_64 ELF toolchain, blocking me
from having both installed simultaneously (see [1] for more
information).

Fortunately, Homebrew provides an i686 ELF toolchain as an official
formulua. Since the i686 cross compiler supports compiling to i386, I'll
use it as the designated toolchain on macOS.

[1] nativeos/homebrew-i386-elf-toolchain#21

Makefile

@@ -13,9 +13,9 @@ OBJECTS += $(patsubst $(SRCDIR)/%.S,$(OUTDIR)/%.S.o,$(ASM_SOURCES))
 
 CXXFLAGS := -m32 -std=c++20 -nostdlib -Wall -Wextra -I $(LIBDIR) \
 			-fno-builtin -fno-exceptions -fno-rtti -fno-use-cxa-atexit
-ASFLAGS =
-LDFLAGS =
-QEMUFLAGS =
+ASFLAGS :=
+LDFLAGS :=
+QEMUFLAGS :=
 
 ifeq ($(DEBUG),1)
 	# Prepend debug flag to make it more prominent
@@ -38,9 +38,23 @@ ifeq ($(UNAME),Linux)
 	ASFLAGS += --32
 	LDFLAGS += -melf_$(ARCH)
 else
-	CXX = $(ARCH)-elf-g++
-	AS = $(ARCH)-elf-as
-	LD = $(ARCH)-elf-ld
+	# Homebrew doesn't provide an i386 ELF toolchain as an official formula,
+	# though one is available from the tap `nativeos/i386-elf-toolchain`.
+	# Unfortunately, the binaries included in this toolchain conflicts with the
+	# deprecated names for the official x86_64 ELF toolchain, blocking me from
+	# having both installed simultaneously (see [1] for more information).
+	#
+	# Fortunately, Homebrew provides an i686 ELF toolchain as an official
+	# formulua. Since the i686 cross compiler supports compiling to i386, I'll
+	# use it as the designated toolchain on macOS.
+	#
+	# [1] https://github.com/nativeos/homebrew-i386-elf-toolchain/issues/21
+	ARCH_ALIAS = $(if $(findstring i386,$(ARCH)), i686, $(ARCH))
+	CXX = $(ARCH_ALIAS)-elf-g++
+	AS = $(ARCH_ALIAS)-elf-as
+	LD = $(ARCH_ALIAS)-elf-ld
+	ASFLAGS += --32 -march=$(ARCH)
+	LDFLAGS += -melf_$(ARCH)
 endif
 
 .PHONY: kernel iso qemu clean