Various changes and improvements.

[jwt27]

Hey there, I've been hacking your build scripts a bit. The most notable improvements in this branch are:

• No longer download and build mpc/mpfr/gmp libraries separately. Instead we can use a script contrib/download_prerequisites in the gcc source tree.
• Checkpoints added to build system, skipping over some parts which have already been built/configured. This allows a user to resume when errors occur, and also avoids rebuilding binutils when installing a different version of gcc.
• Modular build scripts. The entire build process is handled by script/build.sh. Version name scripts (script/*.*.*) now only contain some version-specific variables. This should make it easier to support new gcc versions when they are released, fix bugs, and add new features.
• New variables MAKE_JOBS and GCC_CONFIGURE_OPTIONS allow a user to run multi-threaded builds, and pass custom options to gcc's ./configure.

Some additional testing will likely be required. For example I don't know if tar -a is supported on all platforms. There may be more issues I'm unaware of.

I've also made various other minor changes and fixes. Please see the commit log and let me know what you think.

[jwt27]

I just pushed some more updates. The build script now allows you to specify which components and versions to install or upgrade. I also added support for building gdb.
So for example, to build gcc version 7.1 with the latest binutils and gdb, you would use:
./build-djgpp.sh base binutils gcc-7.1.0 gdb

To just install the latest version of everything, you can use:
./build-djgpp.sh all

Let me know what you think.

[jwt27]

I pushed another update on a new branch: tar. This branch builds GNU tar if it's not installed, so we can unpack all files with -a and no longer need to patch unpack-gcc.sh for OSX.
This will need to be tested by someone on OSX since I'm unable to build tar on my mingw system.

[lhzdem]

谢谢