powerpc: Add back __ARCH_WANT_SYS_LLSEEK macro

This partially reverts commit caf6f9c8 ("asm-generic: Remove
unneeded __ARCH_WANT_SYS_LLSEEK macro")

When CONFIG_COMPAT is disabled on ppc64 the kernel does not build.

There is resistance to both removing the llseek syscall from the 64bit
syscall tables and building the llseek interface unconditionally.
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/lkml/20190828151552.GA16855@infradead.org/
Link: https://lore.kernel.org/lkml/20190829214319.498c7de2@naga/
Link: https://lore.kernel.org/r/dd4575c51e31766e87f7e7fa121d099ab78d3290.1584699455.git.msuchanek@suse.de

arch/powerpc/include/asm/unistd.h

@@ -31,6 +31,7 @@
 #define __ARCH_WANT_SYS_SOCKETCALL
 #define __ARCH_WANT_SYS_FADVISE64
 #define __ARCH_WANT_SYS_GETPGRP
+#define __ARCH_WANT_SYS_LLSEEK
 #define __ARCH_WANT_SYS_NICE
 #define __ARCH_WANT_SYS_OLD_GETRLIMIT
 #define __ARCH_WANT_SYS_OLD_UNAME

fs/read_write.c

@@ -331,7 +331,8 @@ COMPAT_SYSCALL_DEFINE3(lseek, unsigned int, fd, compat_off_t, offset, unsigned i
 }
 #endif
 
-#if !defined(CONFIG_64BIT) || defined(CONFIG_COMPAT)
+#if !defined(CONFIG_64BIT) || defined(CONFIG_COMPAT) || \
+	defined(__ARCH_WANT_SYS_LLSEEK)
 SYSCALL_DEFINE5(llseek, unsigned int, fd, unsigned long, offset_high,
 		unsigned long, offset_low, loff_t __user *, result,
 		unsigned int, whence)