Bug 1499663 - Build grcov so it's compatible with older libstdc++ versions. r=calixte DONTBUILD

Differential Revision: https://phabricator.services.mozilla.com/D103896

taskcluster/scripts/misc/build-grcov.sh

@@ -12,6 +12,7 @@ Linux)
     export CC=clang
     export CXX=clang++
     export RUSTFLAGS=-Clinker=clang++
+    export CXXFLAGS=-D_GLIBCXX_USE_CXX11_ABI=0
 
     export PATH="$MOZ_FETCHES_DIR/clang/bin:$MOZ_FETCHES_DIR/binutils/bin:$PATH"
     ;;