[BUG] Add missing <linux/string.h> include for strcmp.

[H. Nikolaus Schaller]

Hi,
starting with v6.1-rc7 I can't build my tree any more:

  HOSTCC  scripts/mod/modpost.o - due to target missing
In file included from include/linux/string.h:5,
                 from scripts/mod/../../include/linux/license.h:5,
                 from scripts/mod/modpost.c:24:
include/linux/compiler.h:246:10: fatal error: asm/rwonce.h: No such file or directory
  246 | #include <asm/rwonce.h>
      |          ^~~~~~~~~~~~~~
compilation terminated.

Bisect did show your patch as the first bad one:

commit 50c697215a8c "Add missing <linux/string.h> include for strcmp."

Reverting it makes compile succeed.

The problem is that HOSTCC is not necessarily the same compiler or even
architecture as CC and pulling in <linux/compiler.h> or <asm/rwonce.h>
files indirectly isn't a good idea then.

My toolchain is providing HOSTCC = gcc (MacPorts) and CC = arm-linux-gnueabihf
(built from gcc source) and all running on Darwin.

If I change the include to <string.h> I can then "HOSTCC scripts/mod/modpost.c"
but then it fails for "CC kernel/module/main.c" not finding <string.h>:

  CC      kernel/module/main.o - due to target missing
In file included from kernel/module/main.c:43:0:
./include/linux/license.h:5:20: fatal error: string.h: No such file or directory
 #include <string.h>
                    ^
compilation terminated.

So this should be a conditional include depending on CC vs. HOSTCC.
Or moved elsewhere.

BR and thanks,
Nikolaus