I have been struggling lately to find good resources to compile and change OpenJDK. There is a problem with Mac OS Yosemite as it uses Clang as the compiler. But Open JDK 9 builds without a problem. I am adding useful resources here just incase someone finds it useful.
How to build it
1) hg clone http://hg.openjdk.java.net/jdk9/jdk9 jdk9
2) cd ./jdk9
3) bash ./get_source.sh (This will take sometime to download the sources so be patient. May be few hours sometimes)
4) when you try to issue command ./configure you will get the following issue.
configure: error: Could not find freetype! configure exiting with result code 1
5) You need install Xquartz to eliminate the above issue.
6) type make all to build the system. In the make file you can see different options to build the system.
7) Built image will be available usually at at build/macosx-x86_64-normal-server-release/jdk/
If you are trying on Mavericks i could find the following resource which seems to be useful but did not verify whether it actually works 100%