Make event_debug_get_logging_mask_() real symbol (win32)

I cannot made it work without this, even though dumpbin shows that that symbol
exists in the event_core.dll, event_extra.dll failed to compile:
==> win:      Creating library C:/vagrant/.cmake-vagrant/lib/Debug/event_extra.lib and object C:/vagrant/.cmake-vagrant/lib/Debug/event_extra.exp
==> win: http.obj : error LNK2001: unresolved external symbol _event_debug_logging_mask_ [C:\vagrant\.cmake-vagrant\event_extra_shared.vcxproj]
==> win: C:\vagrant\.cmake-vagrant\bin\Debug\event_extra.dll : fatal error LNK1120: 1 unresolved externals [C:\vagrant\.cmake-vagrant\event_extra_shared.vcxproj]
==> win: Done Building Project "C:\vagrant\.cmake-vagrant\event_extra_shared.vcxproj" (default targets) -- FAILED.

And dumpbin:
  sh-4.1$ /cygdrive/c/Program\ Files\ \(x86\)/Microsoft\ Visual\ Studio\ 12.0/VC/bin/amd64/dumpbin.exe /EXPORTS ./bin/Debug/event_core.dll
M
    202   C9 00059A3C event_debug_logging_mask_ = _event_debug_logging_mask_

1 files changed, 6 insertions, 0 deletions

diff --git a/log.c b/log.c
index a9debb86..5a55ab75 100644
--- a/log.c
+++ b/log.c
@@ -70,6 +70,12 @@ static event_fatal_cb fatal_fn = NULL;
 #endif
 
 EVENT2_EXPORT_SYMBOL ev_uint32_t event_debug_logging_mask_ = DEFAULT_MASK;
+
+EVENT2_EXPORT_SYMBOL
+int event_debug_get_logging_mask_()
+{
+	return event_debug_logging_mask_;
+}
 #endif /* EVENT_DEBUG_LOGGING_ENABLED */
 
 void