Initialize OpenCL device on the main thread when pre-compiling kernels.

Else it would cause extremely hard-to-debug random crashes when interpreting
formulas with OpenCL.

And let's re-enable kernel pre-compilation with this fix.

Change-Id: Ib104bfdc3f56a02c052c837eb4bf3ecc95d562e0

sc/source/core/data/formulacell.cxx

@@ -54,7 +54,7 @@
 
 #include <boost/scoped_ptr.hpp>
 
-#define ENABLE_THREADED_OPENCL_KERNEL_COMPILATION 0
+#define ENABLE_THREADED_OPENCL_KERNEL_COMPILATION 1
 
 using namespace formula;
 

sc/source/core/tool/clkernelthread.cxx

@@ -69,6 +69,11 @@ void CLBuildKernelThread::push(CLBuildKernelWorkItem item)
     osl::MutexGuard guard(maQueueMutex);
     maQueue.push(item);
     maQueueCondition.set();
+
+    // This is only to ensure that the OpenCL parameters are initialized on
+    // the main thread before spawning a worker thread for kernel
+    // pre-compilation.
+    sc::FormulaGroupInterpreter::getStatic();
 }
 
 void CLBuildKernelThread::produce()