Update dev guide to fix clang linking issue on arm (opensearch-projec…

…t#1746)

* updated dev guide to fix clang linking issue on arm

Signed-off-by: Finn Roblin <finnrobl@amazon.com>

* restore clang instructions and add additional msg to use gcc if clang linker error

Signed-off-by: Finn Roblin <finnrobl@amazon.com>

* update changelog

Signed-off-by: Finn Roblin <finnrobl@amazon.com>

---------

Signed-off-by: Finn Roblin <finnrobl@amazon.com>

CHANGELOG.md

@@ -18,5 +18,6 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Bug Fixes
 ### Infrastructure
 ### Documentation
+* Update dev guide to fix clang linking issue on arm [#1746](https://github.com/opensearch-project/k-NN/pull/1746)
 ### Maintenance
 ### Refactoring

DEVELOPER_GUIDE.md

@@ -102,7 +102,7 @@ cd jni
 sed -i -e 's/\/usr\/local\/opt\/libomp\//\/opt\/homebrew\/opt\/llvm\//g' cmake/init-faiss.cmake
 sed -i -e 's/__aarch64__/__undefine_aarch64__/g' external/faiss/faiss/utils/distances_simd.cpp
 sed -i -e 's/pragma message WARN/pragma message /g' external/nmslib/similarity_search/src/distcomp_scalar.cc
-// Change -mcpu value to use chip version according to your M series, for example, -mcpu=apple-m1
+// Change -mcpu value to use chip version according to your M series, for example, -mcpu=apple-m1. You can see the supported mcpu values via gcc --print-supported-cpus
 sed -i -e 's/-march=native/-mcpu=apple-m1/g' external/nmslib/similarity_search/CMakeLists.txt
 sed -i -e 's/-mcpu=apple-a14/-mcpu=apple-m1/g' external/nmslib/python_bindings/setup.py
 
@@ -115,6 +115,11 @@ source ~/.zshrc
 export CC=/opt/homebrew/opt/llvm/bin/clang
 export CXX=/opt/homebrew/opt/llvm/bin/clang++
 
+// 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
+
 // Build
 cmake . --fresh
 make
@@ -452,4 +457,4 @@ The Github workflow in [`backport.yml`](.github/workflows/backport.yml) creates
 original PR with an appropriate label `backport <backport-branch-name>` is merged to main with the backport workflow 
 run successfully on the PR. For example, if a PR on main needs to be backported to `1.x` branch, add a label 
 `backport 1.x` to the PR and make sure the backport workflow runs on the PR along with other checks. Once this PR is 
-merged to main, the workflow will create a backport PR to the `1.x` branch.
+merged to main, the workflow will create a backport PR to the `1.x` branch.