System properties: log errno if fsetxattr() fails.

Bug: http://b/386267666
Change-Id: I64453442117dfd0565959d465fa32048f476a4b5
diff --git a/libc/system_properties/prop_area.cpp b/libc/system_properties/prop_area.cpp
index 9b153ca..faa3edf 100644
--- a/libc/system_properties/prop_area.cpp
+++ b/libc/system_properties/prop_area.cpp
@@ -72,7 +72,7 @@
   if (context) {
     if (fsetxattr(fd, XATTR_NAME_SELINUX, context, strlen(context) + 1, 0) != 0) {
       async_safe_format_log(ANDROID_LOG_ERROR, "libc",
-                            "fsetxattr failed to set context (%s) for \"%s\"", context, filename);
+                            "fsetxattr failed to set context (%s) for \"%s\": %m", context, filename);
       /*
        * fsetxattr() will fail during system properties tests due to selinux policy.
        * We do not want to create a custom policy for the tester, so we will continue in