driver: conditionalize use of dlopen functions & use mingw-dlfcn

Not every platform is guaranteed to have dlopen/dlsym, so we should
conditionalize its use. Suprisingly it is actually present for Win32
via the mingw-dlfcn add on, but we should still conditionalize it.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

mingw-libvirt.spec.in

@@ -54,6 +54,8 @@ BuildRequires:  mingw32-libxml2
 BuildRequires:  mingw64-libxml2
 BuildRequires:  mingw32-portablexdr
 BuildRequires:  mingw64-portablexdr
+BuildRequires:  mingw32-dlfcn
+BuildRequires:  mingw64-dlfcn
 
 BuildRequires:  pkgconfig
 # Need native version for msgfmt

src/driver.c

@@ -34,10 +34,11 @@ VIR_LOG_INIT("driver");
 
 
 /* XXX re-implement this for other OS, or use libtools helper lib ? */
-
-#include <dlfcn.h>
 #define DEFAULT_DRIVER_DIR LIBDIR "/libvirt/connection-driver"
 
+#ifdef HAVE_DLFCN_H
+# include <dlfcn.h>
+
 
 static void *
 virDriverLoadModuleFile(const char *file)
@@ -126,6 +127,19 @@ virDriverLoadModuleFull(const char *path,
     return ret;
 }
 
+#else /* ! HAVE_DLFCN_H */
+int
+virDriverLoadModuleFull(const char *path ATTRIBUTE_UNUSED,
+                        const char *regfunc ATTRIBUTE_UNUSED,
+                        void **handle)
+{
+    VIR_DEBUG("dlopen not available on this platform");
+    if (handle)
+        *handle = NULL;
+    return -1;
+}
+#endif /* ! HAVE_DLFCN_H */
+
 
 int
 virDriverLoadModule(const char *name,