parisc: fix building with gcc-15

commit 7cbb015 upstream.

The decompressor is built with the default C dialect, which is now gnu23
on gcc-15, and this clashes with the kernel's bool type definition:

In file included from include/uapi/linux/posix_types.h:5,
                 from arch/parisc/boot/compressed/misc.c:7:
include/linux/stddef.h:11:9: error: cannot use keyword 'false' as enumeration constant
   11 |         false   = 0,

Add the -std=gnu11 argument here, as we do for all other architectures.

Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: arndb

arch/parisc/boot/compressed/Makefile

@@ -18,6 +18,7 @@ KBUILD_CFLAGS += -fno-PIE -mno-space-regs -mdisable-fpregs -Os
 ifndef CONFIG_64BIT
 KBUILD_CFLAGS += -mfast-indirect-calls
 endif
+KBUILD_CFLAGS += -std=gnu11
 
 LDFLAGS_vmlinux := -X -e startup --as-needed -T
 $(obj)/vmlinux: $(obj)/vmlinux.lds $(addprefix $(obj)/, $(OBJECTS)) $(LIBGCC) FORCE