Try to use -Wconditional-uninitialized for clang

https://llvm.org/bugs/show_bug.cgi?id=26640

build/autotools/configure.ac

@@ -46,6 +46,7 @@ if [[ "${ax_cv_prog_cc_fsanitize_address}" = "yes" ]]; then
   LDFLAGS="${LDFLAGS} -fsanitize=address"
 fi
 CXX_FLAG_CHECK([DEBCXXFLAGS], [-fstack-protector-all], [stackprotectorall])
+CXX_FLAG_CHECK([DEBCXXFLAGS], [-Wconditional-uninitialized], [w_conditional_uninitialized])
 CXX_FLAG_CHECK([LDFLAGS], [-static-libstdc++], [static_libstdcxx])
 #CXX_FLAG_CHECK([LDFLAGS], [-static-libgcc], [static_libgcc])