Added instruction for quick syntax check [#CLICKHOUSE-2]

dbms/tests/instructions/syntax.txt

+# Quick syntax check (2 minutes on 16-core server)
+
+mkdir build && cd build
+CC=clang-8 CXX=clang++-8 cmake -D ENABLE_EMBEDDED_COMPILER=0 -D CMAKE_BUILD_TYPE=Debug ..
+ninja re2_st
+time jq --raw-output '.[] | .command' compile_commands.json | grep -P -- ' -o [^ ]+\.o' | grep -v -P -- '-c .+/contrib/' | grep -vP '\.s$' | sed -r -e 's/ -o [^ ]+\.o/ -fsyntax-only/' | sort -R | xargs -I{} -P$(nproc) sh -c '{}'