[libc] Enable automated extraction of error usage reports

Add preprocessor magic to the error definitions to enable every error
usage to be tracked.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/scripts/i386.lds

@@ -162,6 +162,8 @@ SECTIONS {
 	*(.eh_frame.*)
 	*(.rel)
 	*(.rel.*)
+	*(.einfo)
+	*(.einfo.*)
 	*(.discard)
     }