linux-user: move i386/x86_64 signal.c parts to i386 directory

No code change, only move code from signal.c to
i386/signal.c, except adding includes and
exporting setup_frame() and setup_rt_frame().

x86_64/signal.c includes i386/signal.c

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20180424192635.6027-17-laurent@vivier.eu>

linux-user/i386/target_signal.h

@@ -26,4 +26,9 @@ static inline abi_ulong get_sp_from_cpustate(CPUX86State *state)
     return state->regs[R_ESP];
 }
 
+void setup_frame(int sig, struct target_sigaction *ka,
+                 target_sigset_t *set, CPUX86State *env);
+void setup_rt_frame(int sig, struct target_sigaction *ka,
+                    target_siginfo_t *info,
+                    target_sigset_t *set, CPUX86State *env);
 #endif /* I386_TARGET_SIGNAL_H */

linux-user/x86_64/signal.c

@@ -16,3 +16,5 @@
  *  You should have received a copy of the GNU General Public License
  *  along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
+#define I386_TARGET_SIGNAL_H /* to only include x86_64/target_signal.h */
+#include "../i386/signal.c"

linux-user/x86_64/target_signal.h

@@ -26,4 +26,7 @@ static inline abi_ulong get_sp_from_cpustate(CPUX86State *state)
     return state->regs[R_ESP];
 }
 
+void setup_rt_frame(int sig, struct target_sigaction *ka,
+                    target_siginfo_t *info,
+                    target_sigset_t *set, CPUX86State *env);
 #endif /* X86_64_TARGET_SIGNAL_H */