Fix some differences with DXC's disassembly

* We also add an option to tweak our disassembly output to be more easily
  compared with dxc's

renderdoc/maths/formatpacking.cpp

@@ -1281,11 +1281,6 @@ TEST_CASE("Check format conversion", "[format]")
         float f2 = ConvertFromHalf(i2);
         CHECK(!RDCISFINITE(f2));
       }
-      else if(i == 0x8000)
-      {
-        // signed 0
-        CHECK(i2 == 0);
-      }
       else
       {
         CHECK(i == i2);

renderdoc/maths/half_convert.h

@@ -94,7 +94,7 @@ inline float ConvertFromHalf(uint16_t comp)
   if(exponent == 0x00)
   {
     if(mantissa == 0)
-      return 0.0f;
+      return sign ? -0.0f : 0.0f;
 
     // subnormal
     float ret = (float)mantissa;