[build] fix warning of clearing non-trivial type (#5710)

.github/workflows/build.yml

@@ -147,7 +147,7 @@ jobs:
     runs-on: ubuntu-18.04
     strategy:
       matrix:
-        gcc_ver: [5, 6, 7, 8, 9]
+        gcc_ver: [5, 6, 7, 8, 9, 10]
     env:
       CC: gcc-${{ matrix.gcc_ver }}
       CXX: g++-${{ matrix.gcc_ver }}

script/cmake-build

@@ -109,7 +109,7 @@ build()
     mkdir -p "${builddir}"
     cd "${builddir}"
 
-    cmake -GNinja "$@" "${OT_SRCDIR}"
+    cmake -GNinja -DOT_COMPILE_WARNING_AS_ERROR=ON "$@" "${OT_SRCDIR}"
 
     if [[ -n ${OT_CMAKE_NINJA_TARGET[*]} ]]; then
         ninja "${OT_CMAKE_NINJA_TARGET[@]}"

src/core/meshcop/commissioner.cpp

@@ -75,7 +75,7 @@ Commissioner::Commissioner(Instance &aInstance)
     , mJoinerCallback(nullptr)
     , mCallbackContext(nullptr)
 {
-    memset(mJoiners, 0, sizeof(mJoiners));
+    memset(reinterpret_cast<void *>(mJoiners), 0, sizeof(mJoiners));
 
     mCommissionerAloc.Clear();
     mCommissionerAloc.mPrefixLength       = 64;

src/core/thread/network_data_leader_ftd.cpp

@@ -69,7 +69,7 @@ void Leader::Reset(void)
 {
     LeaderBase::Reset();
 
-    memset(mContextLastUsed, 0, sizeof(mContextLastUsed));
+    memset(reinterpret_cast<void *>(mContextLastUsed), 0, sizeof(mContextLastUsed));
     mContextUsed         = 0;
     mContextIdReuseDelay = kContextIdReuseDelay;
 }