[skip ci] Add HAVE_XSL_EXSLT help text (#15174)

Author: petk

ext/xsl/config.m4

@@ -22,7 +22,8 @@ if test "$PHP_XSL" != "no"; then
   [
     PHP_EVAL_INCLINE([$EXSLT_CFLAGS])
     PHP_EVAL_LIBLINE([$EXSLT_LIBS], [XSL_SHARED_LIBADD])
-    AC_DEFINE(HAVE_XSL_EXSLT, 1, [ ])
+    AC_DEFINE([HAVE_XSL_EXSLT], [1],
+      [Define to 1 if system has the EXSLT extension library for XSLT.])
   ], [ ])
 
   AC_DEFINE(HAVE_XSL,1,[ ])

ext/xsl/config.w32

@@ -28,7 +28,7 @@ if (PHP_XSL != "no") {
 		if (ext_xsl_lib_found && CHECK_HEADER_ADD_INCLUDE("libxslt\\xslt.h", "CFLAGS_XSL")) {
 			if (ext_exslt_lib_found) {
 				if (CHECK_HEADER_ADD_INCLUDE("libexslt\\exslt.h", "CFLAGS_XSL")) {
-					AC_DEFINE("HAVE_XSL_EXSLT", 1, "");
+					AC_DEFINE("HAVE_XSL_EXSLT", 1, "Define to 1 if system has the EXSLT extension library for XSLT.");
 				}
 			}
 			EXTENSION("xsl", "php_xsl.c xsltprocessor.c", PHP_XSL_SHARED);