Disable optimizations for gltf_decoder.cc in MSVC builds. (#829)

Not really sure who is to blame, but in optimized builds from MSVC
gltf_decoder.cc appears to be getting garbage values back
from TinyGLTF when it parses the materials for
testdata/.../three_meshes_two_materials_one_no_material.gltf

Since there's no certainty about whether this is limited to this
particular file, just disable optimizations for
src/draco/io/gltf_decoder.cc in all MSVC build configurations.

.github/workflows/ci.yml

@@ -165,11 +165,7 @@ jobs:
                 -DDRACO_TESTS=ON \
                 -DDRACO_TRANSCODER_SUPPORTED=ON
             cmake_build_command: cmake --build . --config Release -- -m:2
-            # TODO(https://github.com/google/draco/issues/826)
-            draco_test_command: |-
-              Release/draco_tests \
-                --gtest_filter=-GltfDecoderTest.ThreeMeshesOneNoMaterialMesh
-
+            draco_test_command: Release/draco_tests
 
           - test_name: windows-msvc-release-static
             os: windows-2019
@@ -189,11 +185,7 @@ jobs:
                 -DDRACO_TESTS=ON \
                 -DDRACO_TRANSCODER_SUPPORTED=ON
             cmake_build_command: cmake --build . --config Release -- -m:2
-            # TODO(https://github.com/google/draco/issues/826)
-            draco_test_command: |-
-              Release/draco_tests \
-                --gtest_filter=-GltfDecoderTest.ThreeMeshesOneNoMaterialMesh
-
+            draco_test_command: Release/draco_tests
 
           - test_name: windows-make-release-shared
             os: windows-2019

CMakeLists.txt

@@ -862,6 +862,13 @@ else()
                     ${draco_include_paths})
 
   if(DRACO_TRANSCODER_SUPPORTED)
+    if(MSVC)
+      # TODO(https://github.com/google/draco/issues/826)
+      set_source_files_properties(
+        "${draco_src_root}/io/gltf_decoder.cc"
+        PROPERTIES COMPILE_OPTIONS "/Od")
+    endif()
+
     draco_add_library(
       NAME
       draco_material