CMakeLists: Make variable shadowing a compile-time error

Now that the entire project is free of variable shadowing, we can enforce this as a compile time error to prevent any further introduction of this logic bug.

src/shader_recompiler/CMakeLists.txt

@@ -253,9 +253,6 @@ else()
         -Werror
         -Werror=conversion
         -Werror=ignored-qualifiers
-        -Werror=implicit-fallthrough
-        -Werror=shadow
-        -Werror=sign-compare
         $<$<CXX_COMPILER_ID:GNU>:-Werror=unused-but-set-parameter>
         $<$<CXX_COMPILER_ID:GNU>:-Werror=unused-but-set-variable>
         -Werror=unused-variable