[support.srcloc.cons] Update xref to [class.mem.general]

The cross-reference to [class.mem] was referring to a hanging paragraph
that was fixed by 2850139 so we should
be referring to [class.mem.general] now.

Author: jwakely

source/support.tex

@@ -3751,7 +3751,7 @@
 \pnum
 \remarks
 Any call to \tcode{current} that appears
-as a default member initializer\iref{class.mem}, or
+as a default member initializer\iref{class.mem.general}, or
 as a subexpression thereof,
 should correspond to the location of
 the constructor definition or aggregate initialization