Update Apex build command

Due to pip having deprecated `--global-option` and `--build-option`,
this will be highly relevant in the future (removal is planned for 23.3,
see pypa/pip#11859).

docs/source/usage_guides/megatron_lm.md

@@ -100,7 +100,10 @@ conda install pytorch torchvision torchaudio cudatoolkit=11.3 -c pytorch
 ```
 git clone https://github.com/NVIDIA/apex
 cd apex
-pip install -v --disable-pip-version-check --no-cache-dir --global-option="--cpp_ext" --global-option="--cuda_ext" ./
+# if pip >= 23.1 (ref: https://pip.pypa.io/en/stable/news/#v23-1) which supports multiple `--config-settings` with the same key... 
+pip install -v --disable-pip-version-check --no-cache-dir --no-build-isolation --config-settings "--build-option=--cpp_ext" --config-settings "--build-option=--cuda_ext" ./
+# otherwise
+pip install -v --disable-pip-version-check --no-cache-dir --no-build-isolation --global-option="--cpp_ext" --global-option="--cuda_ext" ./
 cd ..
 ```
 
@@ -580,4 +583,4 @@ b. Megatron-LM [GPTModel](https://github.com/NVIDIA/Megatron-LM/blob/main/megatr
 c. Megatron-LM [T5Model](https://github.com/NVIDIA/Megatron-LM/blob/main/megatron/model/t5_model.py) : 
 🤗 transformers models with `t5` in  config's model type, e.g., 
 [T5](https://huggingface.co/docs/transformers/model_doc/t5) and 
-[MT5](https://huggingface.co/docs/transformers/model_doc/mt5)
+[MT5](https://huggingface.co/docs/transformers/model_doc/mt5)