SpirvShaderDebugger: Add a virtual destructor
SpirvShaderDebugger: Add a virtual destructor

to debug::Object. This used to be unnecessary as the debug objects used
to contain POD, but we now also have std::string and std::vector fields
in these objects, and we need them to destruct.

Bug: b/148401179
Change-Id: I28637f645a96e3e895e7ae5f3028eb7872c92dd3
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/45608
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Antonio Maiorano <86d87a6550afb6b07035c9743fa181900589f7e0@google.com>
Tested-by: Ben Clayton <1f693eb7158dc33015048c09d6712f74dabddf79@google.com>

bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,google/swiftshader