s390: Add -Wno-pointer-sign to KBUILD_CFLAGS_DECOMPRESSOR

If the decompressor is compiled with clang this can lead to the following
warning:

In file included from arch/s390/boot/startup.c:4:
...
In file included from ./include/linux/pgtable.h:6:
./arch/s390/include/asm/pgtable.h:2065:48: warning: passing 'unsigned long *' to parameter of type
      'long *' converts between pointers to integer types with different sign [-Wpointer-sign]
 2065 |                 value = __atomic64_or_barrier(PGSTE_PCL_BIT, ptr);

Add -Wno-pointer-sign to the decompressor compile flags, like it is also
done for the kernel. This is similar to what was done for x86 to address
the same problem [1].

[1] commit dca5203 ("x86/boot: Add -Wno-pointer-sign to KBUILD_CFLAGS")

Cc: [email protected]
Reported-by: Gerd Bayer <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>
Reviewed-by: Alexander Gordeev <[email protected]>
Signed-off-by: Alexander Gordeev <[email protected]>

Author: hcahca

arch/s390/Makefile

@@ -25,6 +25,7 @@ endif
 KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2 -mpacked-stack -std=gnu11
 KBUILD_CFLAGS_DECOMPRESSOR += -DDISABLE_BRANCH_PROFILING -D__NO_FORTIFY
 KBUILD_CFLAGS_DECOMPRESSOR += -D__DECOMPRESSOR
+KBUILD_CFLAGS_DECOMPRESSOR += -Wno-pointer-sign
 KBUILD_CFLAGS_DECOMPRESSOR += -fno-delete-null-pointer-checks -msoft-float -mbackchain
 KBUILD_CFLAGS_DECOMPRESSOR += -fno-asynchronous-unwind-tables
 KBUILD_CFLAGS_DECOMPRESSOR += -ffreestanding