what is "error: variable 'writable' set but not used [-Werror,-Wunused-but-set-variable]" ?and how fix it?

Question

i want build linphone sdk by below commands but i get error.how fix it?

git clone https://gitlab.linphone.org/BC/public/linphone-sdk.git --recursive
cd linphone-sdk
mkdir build-osx
cmake .. -DLINPHONESDK_PLATFORM=Desktop 
make

and this is error:

how fix it?

-- Build files have been written to: /Users/sia/Desktop/compile1/linphone-sdk/WORK/mac-arm64/Build/ms2
[ 85%] Forcing build for 'EP_ms2'
[ 85%] Performing build step for 'EP_ms2'
[ 0%] Built target ms2-yuv2rgb-vs-header
CMake Warning at /Users/sia/Desktop/compile1/linphone-sdk/linphone-sdk/mac-arm64/share/bctoolbox/cmake/BcGitVersion.cmake:43 (message):
Project version (5.2.0) and git tag (5.2.0-alpha) differ. Please put them
identical

[ 0%] Built target ms2-git-version
[ 0%] Built target ms2-basedescs-header
[ 0%] Built target ms2-voipdescs-header
[ 0%] Built target ms2-fragment-shader-header
[ 0%] Built target ms2-vertex-shader-header
[ 0%] Built target ms2-yuv2rgb-fs-header
Consolidate compiler generated dependencies of target mediastreamer
[ 1%] Building C object src/CMakeFiles/mediastreamer.dir/audiofilters/macsnd.c.o
/Users/sia/Desktop/compile1/linphone-sdk/mediastreamer2/src/audiofilters/macsnd.c:372:10: **error: variable 'writable' set but not used [-Werror,-Wunused-but-set-variable]
Boolean writable;
^**
1 error generated.
make[8]: *** [src/CMakeFiles/mediastreamer.dir/audiofilters/macsnd.c.o] Error 1
make[7]: *** [src/CMakeFiles/mediastreamer.dir/all] Error 2
make[6]: *** [all] Error 2
make[5]: *** [/Users/sia/Desktop/compile1/linphone-sdk/WORK/mac-arm64/Stamp/EP_ms2/EP_ms2-build] Error 2
make[4]: *** [CMakeFiles/EP_ms2.dir/all] Error 2
make[3]: *** [all] Error 2
make[2]: *** [mac-arm64-prefix/src/mac-arm64-stamp/mac-arm64-build] Error 2
make[1]: *** [CMakeFiles/mac-arm64.dir/all] Error 2
make: *** [all] Error 2