CUDA: Fix Cuda.Complex test case extern function signatures

Make the return types of the extern function declared in `main.cpp`
match those in the method implementations.

Tests/Cuda/Complex/main.cpp

@@ -3,8 +3,8 @@
 #include "file1.h"
 #include "file2.h"
 
-result_type call_cuda_seperable_code(int x);
-result_type mixed_launch_kernel(int x);
+int call_cuda_seperable_code(int x);
+int mixed_launch_kernel(int x);
 
 int main(int argc, char** argv)
 {