chore(build) add define to build without expat_config.h

.editorconfig

@@ -12,7 +12,7 @@ indent_size              = 4
 
 [Makefile]
 indent_style             = tab
-indent_size              = 4
+indent_size              = 8
 
 [*.html]
 indent_style             = tab

docs/index.html

@@ -89,6 +89,13 @@ <h2><a name="download"></a>Download</h2>
 <h2><a name="history"></a>History</h2>
 
 <dl class="history">
+	<dt><strong>Version 1.5.x</strong> [unreleased]</dt>
+	<dd>
+		<ul>
+			<li>Fix: allow workaround for <code>expat_config.h</code> not found.</li>
+		</ul>
+	</dd>
+
 	<dt><strong>Version 1.5.1</strong> [03/Oct/2022]</dt>
 	<dd>
 		<ul>

src/lxplib.c

@@ -9,7 +9,17 @@
 #include <stdlib.h>
 #include <string.h>
 
+#ifndef LUAEXPAT_SKIP_EXPAT_CONFIG
+// By default use the standard libexpat header. Some package managers
+// do not include this header. In that case setting LUAEXPAT_SKIP_EXPAT_CONFIG
+// allows you to override the option.
+// 1. ensure you have libExpat 2.4+
+// 2. try building the library
+// 3. try building while defining LUAEXPAT_SKIP_DTD_SUPPORT and XML_DTD (include DTD support)
+// 4. try building while defining LUAEXPAT_SKIP_DTD_SUPPORT (disable DTD support)
 #include "expat_config.h"
+#endif
+
 #include "expat.h"
 #if (XML_MAJOR_VERSION == 2 && XML_MINOR_VERSION < 4) || (XML_MAJOR_VERSION < 2)
 #error Expat 2.4 or newer is required