Build change to support cross architecture modules build

[Alan Bateman]

Mandy Chung wrote:
> Hi Kelly,
>
> This is the build change we discussed to support building modules when 
> the jdk is built for a target architecture different than that of the 
> host system.  Thanks for the suggestion of the make variable names.
>
> Summary:
> jmod needs to run during the modules build to install modules that 
> depends on the jigsaw module system.  jigsaw has native code and hence 
> we can't use the bootclasspath trick for jmod as used by JAVAC_CMD. 
> This fix defines a new JDK_HOST_PATH that set to OUTPUTDIR by default 
> and several HOST_tool_CMD variables.  ALT_JDK_HOST_PATH can be set if 
> needed for cross compilation and it has to be the same version or 
> newer as the built JDK.
>
> Webrev at:
>    http://cr.openjdk.java.net/~mchung/jigsaw/alt-jdk-host-path/
>
> In make/modules/Makefile, thanks for pointing out that  at one point 
> in time, GNU make would exec sh for every line, even if it was a shell 
> comment line.  So I moved the comments  above the target.
>
> Thanks
> Mandy
I've gone through it and it looks good to me.

-Alan.