aarch64: Fix warnings during libgcc build

libgcc/

	* config/aarch64/aarch64-unwind.h (aarch64_cie_signed_with_b_key):
	Add missing const qualifier.  Cast from const unsigned char *
	to const char *.  Use __builtin_strchr to avoid an implicit
	function declaration.
	* config/aarch64/linux-unwind.h (aarch64_fallback_frame_state):
	Add missing cast.

libgcc/config/aarch64/aarch64-unwind.h

@@ -40,8 +40,8 @@ aarch64_cie_signed_with_b_key (struct _Unwind_Context *context)
       const struct dwarf_cie *cie = get_cie (fde);
       if (cie != NULL)
 	{
-	  char *aug_str = cie->augmentation;
-	  return strchr (aug_str, 'B') == NULL ? 0 : 1;
+	  const char *aug_str = (const char *) cie->augmentation;
+	  return __builtin_strchr (aug_str, 'B') == NULL ? 0 : 1;
 	}
     }
   return 0;

libgcc/config/aarch64/linux-unwind.h

@@ -77,7 +77,7 @@ aarch64_fallback_frame_state (struct _Unwind_Context *context,
     }
 
   rt_ = context->cfa;
-  sc = &rt_->uc.uc_mcontext;
+  sc = (struct sigcontext *) &rt_->uc.uc_mcontext;
 
 /* This define duplicates the definition in aarch64.md */
 #define SP_REGNUM 31