Fix DPI undeclared svBitVecVal compile error, bug346.

src/V3EmitCSyms.cpp

@@ -519,6 +519,8 @@ void EmitCSyms::emitDpiHdr() {
     puts("// Manually include this file where DPI .c import functions are declared to insure\n");
     puts("// the C functions match the expectations of the DPI imports.\n");
     puts("\n");
+    puts("#include \"svdpi.h\"\n");
+    puts("\n");
     puts("#ifdef __cplusplus\n");
     puts("extern \"C\" {\n");
     puts("#endif\n");