linux-user: Make target_strerror() return 'const char *'

Make target_strerror() return 'const char *' rather than just 'char *';
this will allow us to return constant strings from it for some special
cases.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>

linux-user/qemu.h

diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 6bd7b32..56f29c3 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -195,7 +195,7 @@
 void gemu_log(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
 extern THREAD CPUState *thread_cpu;
 void cpu_loop(CPUArchState *env);
-char *target_strerror(int err);
+const char *target_strerror(int err);
 int get_osversion(void);
 void init_qemu_uname_release(void);
 void fork_start(void);

linux-user/strace.c

diff --git a/linux-user/strace.c b/linux-user/strace.c
index 0810c85..c5980a1 100644
--- a/linux-user/strace.c
+++ b/linux-user/strace.c
@@ -281,7 +281,7 @@
 static void
 print_syscall_ret_addr(const struct syscallname *name, abi_long ret)
 {
-    char *errstr = NULL;
+    const char *errstr = NULL;
 
     if (ret < 0) {
         errstr = target_strerror(-ret);
@@ -1594,7 +1594,7 @@
 print_syscall_ret(int num, abi_long ret)
 {
     int i;
-    char *errstr = NULL;
+    const char *errstr = NULL;
 
     for(i=0;i<nsyscalls;i++)
         if( scnames[i].nr == num ) {

linux-user/syscall.c

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 7b7bae6..262c645 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -630,7 +630,7 @@
     return (abi_ulong)ret >= (abi_ulong)(-4096);
 }
 
-char *target_strerror(int err)
+const char *target_strerror(int err)
 {
     if ((err >= ERRNO_TABLE_SIZE) || (err < 0)) {
         return NULL;