Need reviewers: update langtools/build.xml

[Jonathan Gibbons]

Ooops,

I omitted reference to the webrev, here: 
http://cr.openjdk.java.net/~jjg/6898585-lt.build/

(Thanks to David for catching that.)

-- Jon

Jonathan Gibbons wrote:
>
> 1. Simplify build macros
>
> Currently, the langtools build.xml builds a number of components (javac,
> javadoc, javah, etc) using a number of macros (build-tool, build-jar,
> build-classes, etc). Currently the macros are such that build-tool 
> invokes
> build-jar which in turn builds build-classes.. This is convenient for
> the use site, since each top level target only needs to invoke a single
> macro to perform its work. However, it is very inconvenient for the
> macro declarations since build-tool has to support all the possible
> parameters for build-jar, and both have to support all the possible
> parameters for build-classes.
>
> Change it so that the macros do not invoke each other but each presumes
> the necessary predecessors have been called. This greatly simplifies
> the macro declarations, and easily compensates for the slightly more
> verbose invocations at the top level targets.  Going forward, it makes
> it much simpler to add new attributes as needed to the various macros.
>
> As a side effect, it also reduces the complexity of any error messages
> reported by Ant, which does not handle errors from nested macro
> invocations particularly gracefully.
>
> 2. Reduce javac invocations in build-classes
>
> The current build-classes macro invokes javac twice, once for the
> generated source, and once for the main source for the tool.  Despite
> its name, the <javac> srcdir attribute defines a "path-like structure",
> meaning that you can provide multiple root directories in which to locate
> the source to be compiled. Using this feature, you can reduce the two
> compilations into a single compilation.
>
> 3. Reduce javac-invocations in build-all-classes
>
> Originally, the rules for building the various langtools tools were
> set up to allow different options (-Xlint, -Werror, etc) for different
> tools. Over time, the tools have been cleaned up to allow uniform
> compilation. While it is still appropriate for the developer targets
> to compile the tools individually, the target invoked by the full JDK
> build can simply compile all the tools together in a single compilation.