Request for review: 7039182 NIO platform specific files

[David Holmes]

http://cr.openjdk.java.net/~dholmes/7039182/webrev/

This will be pushed through the TL jdk repo but Alan suggested getting 
build-dev to review (in addition to himself).

This isn't a public bug so I'll describe the issue.

When the NIO libs are built there are a few files that contain constants 
that represent platform specific I/O constants found in various C header 
files. Normally the build process compiles and runs a small C program 
which will generate the .java file for that platform.

When I integrated the basic support for cross-compilation I modified 
this process to use the host C compiler not the cross-compiler for the 
target, as we couldn't execute the resulting C program. That wasn't the 
correct thing to do because it means we generate values for the build 
platform not the target platform. Luckily these values are mostly the 
same on the Linux platforms we care about, but not all the same (hence 
this bug report where a read system call returned EINVAL because we 
thought we were passing O_NOFOLLOW but in fact passed O_DIRECT).

The simplest fix is to not try to generate a file when cross-compiling 
but allow the developer to specify where these files can be found. This 
is done using the NIO_PLATFORM_CLASSES_ROOT_DIR variable which is 
expected to be the "root" directory for where classes can be found and 
the directories under that are expected to follow the package hierarchy 
for the files, so, for example we will look for:

$(NIO_PLATFORM_CLASSES_ROOT_DIR)/sun/nio/ch/SocketOptionRegistry-$(PLATFORM)-$(ARCH).java

the platform and arch are used in the filename as we don't have 
platform/arch directories in the JDK repo.

In addition I reverted the original change to use the host C compiler as 
this allows you to specifically build the generator program using the 
cross-compiler (which will get the right values) then copy it across to 
the target system and run it to generate the file.

For SE-Embedded we need to set NIO_PLATFORM_CLASSES_ROOT_DIR to point 
into the "closed" platform sources.

Thanks,
David Holmes