x86/syscalls: Add prototypes for C syscall callbacks

.. in order to fix a couple of -Wmissing-prototypes warnings.

No functional change.

 [ bp: Massage commit message and drop newlines. ]
Signed-off-by: Benjamin Thiel <b.thiel@posteo.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200123152754.20149-1-b.thiel@posteo.de

arch/x86/entry/common.c

@@ -34,6 +34,7 @@
 #include <asm/fpu/api.h>
 #include <asm/nospec-branch.h>
 #include <asm/io_bitmap.h>
+#include <asm/syscall.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>

arch/x86/include/asm/syscall.h

@@ -168,6 +168,11 @@ static inline int syscall_get_arch(struct task_struct *task)
 		task->thread_info.status & TS_COMPAT)
 		? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
 }
+
+void do_syscall_64(unsigned long nr, struct pt_regs *regs);
+void do_int80_syscall_32(struct pt_regs *regs);
+long do_fast_syscall_32(struct pt_regs *regs);
+
 #endif	/* CONFIG_X86_32 */
 
 #endif	/* _ASM_X86_SYSCALL_H */