RFR: JDK-8077824: Introduce DefineNativeToolchain to handle toolchain configurations

[Tim Bell]

Erik:

> The macro SetupNativeCompilation handles various overrides of the 
> compiler and linker used for compilation. There is also a LANG option, 
> which implies that it needs to be told if it's compiling C or C++ when 
> in reality, this is handled automatically. The real purpose of the 
> LANG option is just to decide which executable to use for linking in 
> certain conditions/platforms.
>
> I would like to put some more structure around this by introducing a 
> new macro, DefineNativeToolchain. There s a default and a couple of 
> others, extending the default, for linking with the C++ compiler, 
> building for the build platform etc. These definitions will help 
> ensure that all the necessary executables and options are overridden 
> for each of these usecases.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8077824
>
> Webrevs:
>
> The implementation is in NativeCompilation.gmk. I took the liberty of 
> cleaning out some unused compiler/linker variables.
> Top: http://cr.openjdk.java.net/~erikj/8077824/webrev.root.01/
>
> The jdk changes are mostly just removing "LANG:=" and replacing it 
> when necessary with "TOOLCHAIN:=TOOLCHAIN_LINK_CXX". Note that this is 
> not needed for Windows only configurations.
> Jdk: http://cr.openjdk.java.net/~erikj/8077824/webrev.jdk.01/

Nice cleanup.  Looks good to me.

Tim