get breakpad signal handler working on windows

The LibreOffice signal handler overwrites the breakpad signal handler.
Just store the old handler and call that handler before we do any work
in our own handler.

Our own handler implementation is just insane as we are even trying to
take the SolarMutex which can easily deadlock.

Change-Id: I2401bba18701115561d00c7fc11138ead2a48205
Reviewed-on: https://gerrit.libreoffice.org/25022
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

sal/osl/w32/signal.cxx

@@ -18,6 +18,7 @@
  */
 
 #include <sal/config.h>
+#include <config_features.h>
 
 #include <signalshared.hxx>
 
@@ -42,11 +43,13 @@
 namespace
 {
 long WINAPI signalHandlerFunction(LPEXCEPTION_POINTERS lpEP);
+
+LPTOP_LEVEL_EXCEPTION_FILTER pPreviousHandler = nullptr;
 }
 
 bool onInitSignal()
 {
-    SetUnhandledExceptionFilter(signalHandlerFunction);
+    pPreviousHandler = SetUnhandledExceptionFilter(signalHandlerFunction);
 
     HMODULE hFaultRep = LoadLibrary( "faultrep.dll" );
     if ( hFaultRep )
@@ -62,7 +65,7 @@ bool onInitSignal()
 
 bool onDeInitSignal()
 {
-    SetUnhandledExceptionFilter(nullptr);
+    SetUnhandledExceptionFilter(pPreviousHandler);
 
     return false;
 }
@@ -74,6 +77,13 @@ namespace
 
 long WINAPI signalHandlerFunction(LPEXCEPTION_POINTERS lpEP)
 {
+#if HAVE_FEATURE_BREAKPAD
+    // we should make sure to call the breakpad handler as
+    // first step when we hit a problem
+    if (pPreviousHandler)
+        pPreviousHandler(lpEP);
+#endif
+
     static bool bNested = false;
 
     oslSignalInfo info;