On Macosx with this compiler version :

configure: Using clang C compiler version 9.0.0 [Apple LLVM version 9.0.0 (clang-900.0.39.2)

we run into this build error :

/nightly/jdk/src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp:3019:33: error: operator '?:' has lower precedence than '+'; '+' will be evaluated first [-Werror,-Wparentheses]
  return Node::hash() + _native ? 1 : 0;
         ~~~~~~~~~~~~~~~~~~~~~~ ^
/nightly/jdk/src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp:3019:33: note: place parentheses around the '+' expression to silence this warning
  return Node::hash() + _native ? 1 : 0;
                                ^
         ( )
/nightly/jdk/src/hotspot/share/gc/shenandoah/c2/shenandoahSupport.cpp:3019:33: note: place parentheses around the '?:' expression to evaluate it first
  return Node::hash() + _native ? 1 : 0;
                                ^
                        ( )
1 error generated.

This might be related to recent changes :
8227677: Shenandoah: C2: Make in-native LRB special case of normal LRB