fix(luajit): support building on aarch64 hosts

LuaJIT requires its host tools (minilua, buildvm) to match the
target's bitness. On x86_64 hosts this is solved with gcc -m32,
but aarch64 has no equivalent flag.

Use Buildroot's own cross-compiler (TARGET_CC) to build the host
tools as static arm32 binaries, which run natively on aarch64 via
the kernel's 32-bit compat mode (CONFIG_COMPAT). Also use
TARGET_CFLAGS/TARGET_LDFLAGS for the host tools on aarch64, since
HOST_CFLAGS/HOST_LDFLAGS contain aarch64-specific include/library paths
that are wrong for arm32.

Skip selecting BR2_HOSTARCH_NEEDS_IA32_COMPILER on aarch64 since
the IA32 multilib check is not applicable.

Author: bryanforbes

package/batocera/libraries/batocera-luajit/Config.in

@@ -20,7 +20,7 @@ config BR2_PACKAGE_BATOCERA_LUAJIT
 	# luajit.mk uses the "-m32" compiler option to build 32bit
 	# binaries, so check if that option is supported. See
 	# luajit.mk for details.
-	select BR2_HOSTARCH_NEEDS_IA32_COMPILER if !BR2_ARCH_IS_64
+	select BR2_HOSTARCH_NEEDS_IA32_COMPILER if !BR2_ARCH_IS_64 && BR2_HOSTARCH != "aarch64"
 	help
 	  LuaJIT implements the full set of language features defined
 	  by Lua 5.1. The virtual machine (VM) is API- and

package/batocera/libraries/batocera-luajit/batocera-luajit.mk

@@ -28,7 +28,18 @@ ifeq ($(BR2_ARCH_IS_64),y)
 BATOCERA_LUAJIT_HOST_CC = $(HOSTCC)
 # There is no LUAJIT_ENABLE_GC64 option.
 else
+# On aarch64 hosts, there is no -m32 equivalent. Instead, use Buildroot's own
+# cross-compiler to build the host tools (minilua, buildvm) as static arm32
+# binaries, which run natively via the kernel's 32-bit compat mode (CONFIG_COMPAT).
+ifeq ($(HOSTARCH),aarch64)
+BATOCERA_LUAJIT_HOST_CC = $(TARGET_CC) -static
+BATOCERA_LUAJIT_HOST_CFLAGS = $(TARGET_CFLAGS)
+BATOCERA_LUAJIT_HOST_LDFLAGS = $(TARGET_LDFLAGS)
+else
 BATOCERA_LUAJIT_HOST_CC = $(HOSTCC) -m32
+BATOCERA_LUAJIT_HOST_CFLAGS = $(HOST_CFLAGS)
+BATOCERA_LUAJIT_HOST_LDFLAGS = $(HOST_LDFLAGS)
+endif
 BATOCERA_LUAJIT_XCFLAGS += -DLUAJIT_DISABLE_GC64
 endif
 
@@ -44,8 +55,8 @@ define BATOCERA_LUAJIT_BUILD_CMDS
 		TARGET_CFLAGS="$(TARGET_CFLAGS)" \
 		TARGET_LDFLAGS="$(TARGET_LDFLAGS)" \
 		HOST_CC="$(BATOCERA_LUAJIT_HOST_CC)" \
-		HOST_CFLAGS="$(HOST_CFLAGS)" \
-		HOST_LDFLAGS="$(HOST_LDFLAGS)" \
+		HOST_CFLAGS="$(BATOCERA_LUAJIT_HOST_CFLAGS)" \
+		HOST_LDFLAGS="$(BATOCERA_LUAJIT_HOST_LDFLAGS)" \
 		BUILDMODE=dynamic \
 		XCFLAGS="$(BATOCERA_LUAJIT_XCFLAGS)" \
 		-C $(@D) amalg