Fix sed command in DEVELOPER_GUIDE.md to append a new line character '\n'.

[0ctopus13prime]

Description

This PR is to fix the sed command listed in DEVELOPER_GUIDE.md to append a new line after addition.
In the guide, it is recommended to use sed command to append a new line having libomp related CXX arguments in Mac.
However, since the added new line does not end with '\n' making its following sentence to be located right behind the closing parenthesis, resulting in CMake processing failure.

In DEVELOPER_GUIDE.md

...
// In case of linking issues with the external libraries and clang, you can try setting the CMAKE compiler to gcc/g++ instead through the following commands:
export CC=gcc
export CXX=g++
sed -i '' '/set(CMAKE_CXX_STANDARD_REQUIRED True)/a\'$'\n''set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Xclang -fopenmp -L/opt/homebrew/opt/libomp/lib -I/opt/homebrew/opt/libomp/include -lomp -arch arm64 -fexceptions")' CMakeLists.txt
...

Changes

Before: You can see option(... is right behind the closing parenthesis of set(.

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Xclang -fopenmp -L/opt/homebrew/opt/libomp/lib -I/opt/homebrew/opt/libomp/include -lomp -arch arm64 -fexceptions")option(CONFIG_FAISS "Configure faiss library build when this is on")

After: New line '\n' will be added after the closing parenthesis of set(.

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Xclang -fopenmp -L/opt/homebrew/opt/libomp/lib -I/opt/homebrew/opt/libomp/include -lomp -arch arm64 -fexceptions")
option(CONFIG_FAISS "Configure faiss library build when this is on")

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[opensearch-trigger-bot]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-2181-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 677184230bccec01ecfaf43fa3ed368dacf5a510
# Push it to GitHub
git push --set-upstream origin backport/backport-2181-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-2181-to-2.x.

[0ctopus13prime]

Back port PR : #2184