Hotspot can be built without C1 (or C2): --with-jvm-features=-compiler1
But Graal Java JIT requires C1 compiler to compile itself. Otherwise it takes long time to compile first hot methods because Graal have to compile itself and run in Interpreter until then. Few tests timeout in such configuration.
Build code have check for JVMCI but not for Graal:

http://hg.openjdk.java.net/jdk/jdk/file/d8cd1a8ae50f/make/autoconf/hotspot.m4#l324

But that check only work when you specified --with-jvm-features=jvmci and it does not work for case when C1 or C2 is disabled --with-jvm-features=-compiler2. Script should check DISABLED_JVM_FEATURES variable for disabled features.