[PATCH 05/13] sim/m32r: fix unused variable warning on non-Linux hosts

When building on macOS, I get:

    /Users/smarchi/src/binutils-gdb/sim/m32r/traps.c:191:18: error: unused variable 'cb' [-Werror,-Wunused-variable]
      191 |   host_callback *cb = STATE_CALLBACK (sd);
          |                  ^~

All the uses of `cb' in m32r_trap are inside the TRAP_LINUX_SYSCALL
case, which is guarded by `#ifdef __linux__'.  Move the declaration
inside that case, so that it only exists where it is used.

Change-Id: I609850daf7fa60d92856988dffe7e314eb1d8a30
---
 sim/m32r/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sim/m32r/traps.c b/sim/m32r/traps.c
index 7b98b2453972..bb82ae80e2aa 100644
--- a/sim/m32r/traps.c
+++ b/sim/m32r/traps.c
@@ -188,7 +188,6 @@ USI
 m32r_trap (SIM_CPU *current_cpu, PCADDR pc, int num)
 {
   SIM_DESC sd = CPU_STATE (current_cpu);
-  host_callback *cb = STATE_CALLBACK (sd);
 
   if (STATE_ENVIRONMENT (sd) == OPERATING_ENVIRONMENT)
     goto case_default;
@@ -217,6 +216,7 @@ m32r_trap (SIM_CPU *current_cpu, PCADDR pc, int num)
 #ifdef __linux__
     case TRAP_LINUX_SYSCALL:
       {
+	host_callback *cb = STATE_CALLBACK (sd);
 	CB_SYSCALL s;
 	unsigned int func, arg1, arg2, arg3, arg4, arg5, arg6, arg7;
 	int result, errcode;
-- 
2.55.0