I'm checking out the MacOS X devkit on a new MacOS 10.10.5 machine.
This machine does not have Xcode installed.

I've seen the fix for the following bug:

JDK-8138694 Devkit build on Macosx still requires Xcode to be installed

and I'm using today's copy of JDK9-dev which contains that fix.

The build fails in hotspot with the following error:

$ tail -30 make.all.macosx-x86_64-normal-server-release.log
Compiling 66 files for jdk.crypto.pkcs11
Compiling 36 files for jdk.jcmd
Compiling 16 files for jdk.naming.dns
Compiling 6 files for jdk.naming.rmi
Compiling 2728 files for java.desktop
/work/shared/mirrors/src_clones/jdk9/dev_baseline/hotspot/src/os/bsd/vm/jsig.c:33:10: fatal error: 'signal.h' file not found
#include <signal.h>
         ^
1 error generated.
make[10]: *** [libjsig.dylib] Error 1
make[9]: *** [the_vm] Error 2
make[8]: *** [product] Error 2
make[7]: *** [generic_build2] Error 2
make[6]: *** [product] Error 2
make[5]: *** [all_product_universal] Error 2
make[4]: *** [universal_product] Error 2
make[3]: *** [/work/shared/mirrors/src_clones/jdk9/dev_baseline/build/macosx-x86_64-normal-server-release/hotspot/_hotspot.timestamp] Error 2
make[2]: *** [hotspot] Error 2
make[2]: *** Waiting for unfinished jobs....

ERROR: Build failed for target 'all' in configuration 'macosx-x86_64-normal-server-release' (exit code 2)
No indication of failed target found.
Hint: Try searching the build log for '] Error'.
Hint: If caused by a warning, try configure --disable-warnings-as-errors.

make[1]: *** [main] Error 2
make: *** [all] Error 2


Build Finished: Wed Oct 14 16:45:10 MDT 2015