asm-generic: Unify uapi bitsperlong.h for arm64, riscv and loongarch

Now we specify the minimal version of GCC as 5.1 and Clang/LLVM as 11.0.0
in Documentation/process/changes.rst, __CHAR_BIT__ and __SIZEOF_LONG__ are
usable, it is probably fine to unify the definition of __BITS_PER_LONG as
(__CHAR_BIT__ * __SIZEOF_LONG__) in asm-generic uapi bitsperlong.h.

In order to keep safe and avoid regression, only unify uapi bitsperlong.h
for some archs such as arm64, riscv and loongarch which are using newer
toolchains that have the definitions of __CHAR_BIT__ and __SIZEOF_LONG__.

Suggested-by: Xi Ruoyao <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Suggested-by: Arnd Bergmann <[email protected]>
Link: https://lore.kernel.org/linux-arch/[email protected]/
Signed-off-by: Tiezhu Yang <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>

Author: seehearfeel

include/uapi/asm-generic/bitsperlong.h

@@ -1,15 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
 #ifndef _UAPI__ASM_GENERIC_BITS_PER_LONG
 #define _UAPI__ASM_GENERIC_BITS_PER_LONG
 
+#ifndef __BITS_PER_LONG
+/*
+ * In order to keep safe and avoid regression, only unify uapi
+ * bitsperlong.h for some archs which are using newer toolchains
+ * that have the definitions of __CHAR_BIT__ and __SIZEOF_LONG__.
+ * See the following link for more info:
+ * https://lore.kernel.org/linux-arch/[email protected]/
+ */
+#if defined(__CHAR_BIT__) && defined(__SIZEOF_LONG__)
+#define __BITS_PER_LONG (__CHAR_BIT__ * __SIZEOF_LONG__)
+#else
 /*
  * There seems to be no way of detecting this automatically from user
  * space, so 64 bit architectures should override this in their
  * bitsperlong.h. In particular, an architecture that supports
  * both 32 and 64 bit user space must not rely on CONFIG_64BIT
  * to decide it, but rather check a compiler provided macro.
  */
-#ifndef __BITS_PER_LONG
 #define __BITS_PER_LONG 32
 #endif
+#endif
 
 #endif /* _UAPI__ASM_GENERIC_BITS_PER_LONG */