tools: Add LoongArch build infrastructure

We will add tools support for LoongArch (bpf, perf, objtool, etc.), add
build infrastructure and common headers for preparation.
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

tools/arch/loongarch/include/uapi/asm/bitsperlong.h

+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef __ASM_LOONGARCH_BITSPERLONG_H
+#define __ASM_LOONGARCH_BITSPERLONG_H
+
+#define __BITS_PER_LONG (__SIZEOF_POINTER__ * 8)
+
+#include <asm-generic/bitsperlong.h>
+
+#endif /* __ASM_LOONGARCH_BITSPERLONG_H */

tools/scripts/Makefile.arch

@@ -5,7 +5,7 @@ HOSTARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
                                   -e s/s390x/s390/ -e s/parisc64/parisc/ \
                                   -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
                                   -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ \
-                                  -e s/riscv.*/riscv/)
+                                  -e s/riscv.*/riscv/ -e s/loongarch.*/loongarch/)
 
 ifndef ARCH
 ARCH := $(HOSTARCH)
@@ -34,6 +34,15 @@ ifeq ($(ARCH),sh64)
        SRCARCH := sh
 endif
 
+# Additional ARCH settings for loongarch
+ifeq ($(ARCH),loongarch32)
+       SRCARCH := loongarch
+endif
+
+ifeq ($(ARCH),loongarch64)
+       SRCARCH := loongarch
+endif
+
 LP64 := $(shell echo __LP64__ | ${CC} ${CFLAGS} -E -x c - | tail -n 1)
 ifeq ($(LP64), 1)
   IS_64_BIT := 1