move signal.h definition of stack_t to arch-specific bits

it's different at least on mips. mips version will be fixed in a
separate commit to show the change.

arch/arm/bits/signal.h

@@ -27,6 +27,12 @@ typedef struct __ucontext {
 	unsigned long long uc_regspace[64];
 } ucontext_t;
 
+typedef struct sigaltstack {
+	void *ss_sp;
+	int ss_flags;
+	size_t ss_size;
+} stack_t;
+
 #define SA_NOCLDSTOP  1
 #define SA_NOCLDWAIT  2
 #define SA_SIGINFO    4

arch/i386/bits/signal.h

@@ -62,6 +62,12 @@ typedef struct __ucontext {
 	unsigned long __fpregs_mem[28];
 } ucontext_t;
 
+typedef struct sigaltstack {
+	void *ss_sp;
+	int ss_flags;
+	size_t ss_size;
+} stack_t;
+
 #define SA_NOCLDSTOP  1
 #define SA_NOCLDWAIT  2
 #define SA_SIGINFO    4

arch/microblaze/bits/signal.h

@@ -29,6 +29,12 @@ typedef struct __ucontext {
 	sigset_t uc_sigmask;
 } ucontext_t;
 
+typedef struct sigaltstack {
+	void *ss_sp;
+	int ss_flags;
+	size_t ss_size;
+} stack_t;
+
 #define SA_NOCLDSTOP  1
 #define SA_NOCLDWAIT  2
 #define SA_SIGINFO    4

arch/mips/bits/signal.h

@@ -46,6 +46,12 @@ typedef struct __ucontext {
 	sigset_t uc_sigmask;
 } ucontext_t;
 
+typedef struct sigaltstack {
+	void *ss_sp;
+	int ss_flags;
+	size_t ss_size;
+} stack_t;
+
 #define SA_NOCLDSTOP  1
 #define SA_NOCLDWAIT  0x10000
 #define SA_SIGINFO    8

arch/powerpc/bits/signal.h

@@ -60,6 +60,12 @@ typedef struct __ucontext {
 	mcontext_t uc_mcontext;
 } ucontext_t;
 
+typedef struct sigaltstack {
+	void *ss_sp;
+	int ss_flags;
+	size_t ss_size;
+} stack_t;
+
 #define SA_NOCLDSTOP  1U
 #define SA_NOCLDWAIT  2U
 #define SA_SIGINFO    4U

arch/sh/bits/signal.h

@@ -27,6 +27,12 @@ typedef struct __ucontext {
 	sigset_t uc_sigmask;
 } ucontext_t;
 
+typedef struct sigaltstack {
+	void *ss_sp;
+	int ss_flags;
+	size_t ss_size;
+} stack_t;
+
 #define SA_NOCLDSTOP  1
 #define SA_NOCLDWAIT  2
 #define SA_SIGINFO    4

arch/x32/bits/signal.h

@@ -69,6 +69,12 @@ typedef struct __ucontext {
 	unsigned long long __fpregs_mem[64];
 } ucontext_t;
 
+typedef struct sigaltstack {
+	void *ss_sp;
+	int ss_flags;
+	size_t ss_size;
+} stack_t;
+
 #define SA_NOCLDSTOP  1
 #define SA_NOCLDWAIT  2
 #define SA_SIGINFO    4

arch/x86_64/bits/signal.h

@@ -69,6 +69,12 @@ typedef struct __ucontext {
 	unsigned long __fpregs_mem[64];
 } ucontext_t;
 
+typedef struct sigaltstack {
+	void *ss_sp;
+	int ss_flags;
+	size_t ss_size;
+} stack_t;
+
 #define SA_NOCLDSTOP  1
 #define SA_NOCLDWAIT  2
 #define SA_SIGINFO    4

include/signal.h

@@ -77,12 +77,6 @@ extern "C" {
 #define CLD_STOPPED 5
 #define CLD_CONTINUED 6
 
-typedef struct sigaltstack {
-	void *ss_sp;
-	int ss_flags;
-	size_t ss_size;
-} stack_t;
-
 union sigval {
 	int sival_int;
 	void *sival_ptr;