gcc before 4.8.x does not have winhttp library

It has a partial winhttp.h header, but not the associated library,
so we won't try to build anything based on winhttp there.

Author: craigberry

Win32.pm

@@ -1305,6 +1305,14 @@ of hex digits with surrounding braces.  For example:
 
     {09531CF1-D0C7-4860-840C-1C8C8735E2AD}
 
+=item Win32::HttpGetFile(URL, FILENAME)
+
+Uses the WinHttp library to download the file specified by the URL
+parameter to the local file specified by FILENAME. Only http and https
+protocols are supported.  Authentication is not supported.  The function
+is not available when building with gcc prior to 4.8.0 because the
+winhttp library is not available.
+
 =item Win32::InitiateSystemShutdown
 
 (MACHINE, MESSAGE, TIMEOUT, FORCECLOSE, REBOOT)
@@ -1472,12 +1480,6 @@ instead.
 Loads the DLL LIBRARYNAME and calls the function
 DllUnregisterServer.
 
-=item Win32::HttpGetFile(URL, FILENAME)
-
-Uses the WinHttp library to download the file specified by the URL
-parameter to the local file specified by FILENAME. Only http and https
-protocols are supported.  Authentication is not supported.
-
 =back
 
 =head1 CAVEATS

Win32.xs

@@ -7,7 +7,9 @@
 #include <wchar.h>
 #include <userenv.h>
 #include <lm.h>
-#include <winhttp.h>
+#if !defined(__GNUC__) || (((100000 * __GNUC__) + (1000 * __GNUC_MINOR__)) >= 408000)
+#  include <winhttp.h>
+#endif
 
 #define PERL_NO_GET_CONTEXT
 #include "EXTERN.h"
@@ -1683,6 +1685,7 @@ XS(w32_IsDeveloperModeEnabled)
     XSRETURN_NO;
 }
 
+#ifdef WINHTTPAPI
 
 XS(w32_HttpGetFile)
 {
@@ -1902,6 +1905,8 @@ XS(w32_HttpGetFile)
     XSRETURN_YES;
 }
 
+#endif
+
 MODULE = Win32            PACKAGE = Win32
 
 PROTOTYPES: DISABLE
@@ -1976,6 +1981,8 @@ BOOT:
 #ifdef __CYGWIN__
     newXS("Win32::SetChildShowWindow", w32_SetChildShowWindow, file);
 #endif
+#ifdef WINHTTPAPI
     newXS("Win32::HttpGetFile", w32_HttpGetFile, file);
+#endif
     XSRETURN_YES;
 }

t/HttpGetFile.t

@@ -7,6 +7,11 @@ use Digest::SHA;
 my $tmpfile = "http-download-test-$$.tgz";
 END { 1 while unlink $tmpfile; }
 
+unless (defined &Win32::HttpGetFile) {
+    print "1..0 # Skip: gcc before 4.8 does not have winhttp library\n";
+    exit;
+}
+
 # We may not always have an internet connection, so don't
 # attempt remote connections unless the user has done
 #   set PERL_WIN32_INTERNET_OK=1