arm: Fix warning in libgcc/config/arm/pr-support.c

I have noticed some warnings when building GCC for arm-eabi:
pr-support.c:110:7: warning: variable ‘set_pac_sp’ set but not used [-Wunused-but-set-variable]
pr-support.c:109:7: warning: variable ‘set_pac’ set but not used [-Wunused-but-set-variable]

This small patch avoids them by defining these two variables undef
TARGET_HAVE_PACBTI, like the code which actually uses them.

	libgcc/
	* config/arm/pr-support.c (__gnu_unwind_execute): Use
	TARGET_HAVE_PACBTI to define set_pac and set_pac_sp.

libgcc/config/arm/pr-support.c

@@ -106,8 +106,10 @@ __gnu_unwind_execute (_Unwind_Context * context, __gnu_unwind_state * uws)
 {
   _uw op;
   int set_pc;
+#if defined(TARGET_HAVE_PACBTI)
   int set_pac = 0;
   int set_pac_sp = 0;
+#endif
   _uw reg;
   _uw sp;
 
@@ -258,7 +260,9 @@ __gnu_unwind_execute (_Unwind_Context * context, __gnu_unwind_state * uws)
 	      if (_Unwind_VRS_Pop (context, _UVRSC_PAC, 0, _UVRSD_UINT32)
 		  != _UVRSR_OK)
 		return _URC_FAILURE;
+#if defined(TARGET_HAVE_PACBTI)
 	      set_pac = 1;
+#endif
 	      continue;
 	    }
 
@@ -266,7 +270,9 @@ __gnu_unwind_execute (_Unwind_Context * context, __gnu_unwind_state * uws)
 	  if (op == 0xb5)
 	    {
 	      _Unwind_VRS_Get (context, _UVRSC_CORE, R_SP, _UVRSD_UINT32, &sp);
+#if defined(TARGET_HAVE_PACBTI)
 	      set_pac_sp = 1;
+#endif
 	      continue;
 	    }