[ctime.syn] Improve indexing for macros

Author: AlisdairM

source/time.tex

@@ -11606,9 +11606,6 @@
 \rSec1[ctime.syn]{Header \tcode{<ctime>} synopsis}
 
 \indexheader{ctime}%
-\indexlibraryglobal{CLOCKS_PER_SEC}%
-\indexlibraryglobal{NULL}%
-\indexlibraryglobal{TIME_UTC}%
 \indexlibraryglobal{asctime}%
 \indexlibraryglobal{clock_t}%
 \indexlibraryglobal{clock}%
@@ -11625,9 +11622,9 @@
 \indexlibraryglobal{time}%
 \indexlibraryglobal{tm}%
 \begin{codeblock}
-#define NULL @\textit{see \ref{support.types.nullptr}}@
-#define CLOCKS_PER_SEC @\seebelow@
-#define TIME_UTC @\seebelow@
+#define @\libmacro{NULL}@ @\textit{see \ref{support.types.nullptr}}@
+#define @\libmacro{CLOCKS_PER_SEC}@ @\seebelow@
+#define @\libmacro{TIME_UTC}@ @\seebelow@
 
 namespace std {
   using size_t = @\textit{see \ref{support.types.layout}}@;