linux-user/signal.c: Create a common rewind_if_in_safe_syscall

All instances of rewind_if_in_safe_syscall are the same, differing only
in how the instruction point is fetched from the ucontext and the size
of the registers. Use host_signal_pc and new host_signal_set_pc
interfaces to fetch the pointer to the PC and adjust if needed. Delete
all the old copies of rewind_if_in_safe_syscall.

Acked-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20211113045603.60391-3-imp@bsdimp.com>
[rth: include safe-syscall.h, simplify ifdefs]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
diff --git a/linux-user/safe-syscall.h b/linux-user/safe-syscall.h
index 6bc0390..aaa9ffc 100644
--- a/linux-user/safe-syscall.h
+++ b/linux-user/safe-syscall.h
@@ -127,6 +127,9 @@
 #ifdef HAVE_SAFE_SYSCALL
 /* The core part of this function is implemented in assembly */
 extern long safe_syscall_base(int *pending, long number, ...);
+/* These are defined by the safe-syscall.inc.S file */
+extern char safe_syscall_start[];
+extern char safe_syscall_end[];
 
 #define safe_syscall(...)                                               \
     ({                                                                  \