Never specify /O1

Leaving it as /O2 might improve performance.
Stops this from being spammed:
cl : command line  warning D9025: overriding '/O2' with '/O1' [D:\a\xenia-canary\xenia-canary\build\glslang-spirv.vcxproj]

/Os is implied by /O1;
https://learn.microsoft.com/en-us/cpp/build/reference/o1-o2-minimize-size-maximize-speed?view=msvc-170

third_party/imgui.lua

@@ -11,12 +11,11 @@ project("imgui")
   includedirs({
     "imgui",
   })
-  filter({"configurations:Release", "platforms:Windows"})
-    buildoptions({
-      "/Os",
-      "/O1"
-    })
-  filter{}
+--  filter({"configurations:Release", "platforms:Windows"})
+--    buildoptions({
+--      "/O1",
+--    })
+--  filter{}
   files({
     "imgui/imconfig.h",
     "imgui/imgui.cpp",