Switch the default of reverse translation to emitting opaque pointers. (#2074)

Most of the changes are adding -emit-opaque-pointers=0 lines to test
code. The code generally works in the forward translation at this point,
although there is still substantial work that needs to be done to finish
porting the tests.

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@10b1354

Author: jcranmer-intel

llvm-spirv/tools/llvm-spirv/llvm-spirv.cpp

@@ -161,8 +161,7 @@ constexpr static bool SPIRVOpaquePointersDefault = false;
 #endif
 
 static cl::opt<bool>
-    EmitOpaquePointers("emit-opaque-pointers",
-                       cl::init(SPIRVOpaquePointersDefault),
+    EmitOpaquePointers("emit-opaque-pointers", cl::init(true),
                        cl::desc("Emit opaque instead of typed LLVM pointers "
                                 "for the translation from SPIR-V."),
                        cl::Hidden);