Fix zlib support on MS-Windows.

 configure.ac (HAVE_ZLIB): Don't use -lz on MinGW.

 src/decompress.c <zlib_initialized> [WINDOWSNT]: New static variable.
 (Fzlib_decompress_region) [WINDOWSNT]: Call init_zlib_functions if
 not yet initialized.

ChangeLog

+2013-08-12  Eli Zaretskii  <eliz@gnu.org>
+
+	* configure.ac (HAVE_ZLIB): Don't use -lz on MinGW.
+
 2013-08-12  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Minor zlib configuration tweaks.

configure.ac

@@ -2955,6 +2955,10 @@ if test "${with_zlib}" != "no"; then
 fi
 if test "${HAVE_ZLIB}" = "yes"; then
   AC_DEFINE([HAVE_ZLIB], 1, [Define to 1 if you have the zlib library (-lz).])
+  ### mingw32 doesn't use -lz, since it loads the library dynamically.
+  if test "${opsys}" = "mingw32"; then
+     LIBZ=
+  fi
 fi
 AC_SUBST(LIBZ)
 

src/ChangeLog

+2013-08-12  Eli Zaretskii  <eliz@gnu.org>
+
+	* decompress.c <zlib_initialized> [WINDOWSNT]: New static variable.
+	(Fzlib_decompress_region) [WINDOWSNT]: Call init_zlib_functions if
+	not yet initialized.
+
 2013-08-12  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
 	* decompress.c (Fzlib_decompress_region): Support zlib

src/decompress.c

@@ -38,7 +38,7 @@ static Lisp_Object Qzlib_dll;
 /* Macro for loading zlib functions from the library.  */
 #define LOAD_ZLIB_FN(lib,func) {					\
     fn_##func = (void *) GetProcAddress (lib, #func);			\
-    if (!fn_##func) return 0;						\
+    if (!fn_##func) return false;					\
   }
 
 DEF_ZLIB_FN (int, inflateInit2_,
@@ -50,6 +50,8 @@ DEF_ZLIB_FN (int, inflate,
 DEF_ZLIB_FN (int, inflateEnd,
 	     (z_streamp strm));
 
+static bool zlib_initialized;
+
 static bool
 init_zlib_functions (void)
 {
@@ -58,13 +60,13 @@ init_zlib_functions (void)
   if (!library)
     {
       message1 ("zlib library not found");
-      return 0;
+      return false;
     }
 
   LOAD_ZLIB_FN (library, inflateInit2_);
   LOAD_ZLIB_FN (library, inflate);
   LOAD_ZLIB_FN (library, inflateEnd);
-  return 1;
+  return true;
 }
 
 #define fn_inflateInit2(strm, windowBits) \
@@ -139,6 +141,11 @@ This function can be called only in unibyte buffers.  */)
   if (! NILP (BVAR (current_buffer, enable_multibyte_characters)))
     error ("This function can be called only in unibyte buffers");
 
+#ifdef WINDOWSNT
+  if (!zlib_initialized)
+    zlib_initialized = init_zlib_functions ();
+#endif
+
   /* This is a unibyte buffer, so character positions and bytes are
      the same.  */
   istart = XINT (start);