Only use -Wgnu-empty-initializer on Clang and not GCC.

Broken by ee566eb880.

PiperOrigin-RevId: 517390165
Change-Id: Ibd8ec46647873050899cffe435e3f5c293279aae

cmake/MujocoOptions.cmake

@@ -93,7 +93,6 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR (CMAKE_CXX_COMPILER_ID MATCHES "Clang
       -Wno-int-in-bool-context
       -Wno-sign-compare
       -Wno-unknown-pragmas
-      -Wgnu-empty-initializer
   )
   if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
     # Set -Wimplicit-fallthrough=5 to only allow fallthrough annotation via __attribute__.
@@ -101,6 +100,9 @@ if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR (CMAKE_CXX_COMPILER_ID MATCHES "Clang
                               -Wno-maybe-uninitialized
     )
   endif()
+  if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT MSVC)
+    set(EXTRA_COMPILE_OPTIONS ${EXTRA_COMPILE_OPTIONS} -Wgnu-empty-initializer)
+  endif()
 endif()
 
 if(WIN32)