linux-user/mips/o32: Drop sa_restorer functionality

The Linux kernel dropped support for sa_restorer on O32 MIPS in the
release 2.5.48 because it was unused. See the comment in
arch/mips/include/uapi/asm/signal.h.

Applications using the kernels UAPI headers will not reserve enough
space for qemu-user to copy the sigaction.sa_restorer field to.
Unrelated data may be overwritten.

Align qemu-user with the kernel by also dropping sa_restorer support.

Signed-off-by: Thomas Weißschuh <thomas@t-8ch.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20250709-mips-sa-restorer-v1-1-fc17120e4afe@t-8ch.de>

linux-user/mips/target_signal.h

@@ -64,7 +64,6 @@ typedef struct target_sigaltstack {
 #define TARGET_SA_NODEFER       0x40000000
 #define TARGET_SA_RESTART       0x10000000
 #define TARGET_SA_RESETHAND     0x80000000
-#define TARGET_SA_RESTORER      0x04000000      /* Only for O32 */
 
 #define TARGET_MINSIGSTKSZ    2048
 

linux-user/syscall_defs.h

@@ -515,10 +515,6 @@ struct target_sigaction {
     abi_ulong       _sa_handler;
 #endif
     target_sigset_t sa_mask;
-#ifdef TARGET_ARCH_HAS_SA_RESTORER
-    /* ??? This is always present, but ignored unless O32.  */
-    abi_ulong sa_restorer;
-#endif
 };
 #else
 struct target_old_sigaction {