- run as bash script (since Debian's new 'dash' shell doesn't support it)
- remove obsolete host GCC requirement
- improve Windows support by using better heuristics for the executable suffix
- better NDK root directory auto-detection (avoids the need to define ANDROID_NDK_ROOT on some installs)
This is used to reduce the number of distributable prebuilt packages
(i.e. linux-x86_64 is not needed anymore).
Also fix build/tools/build-toolchain.sh to properly copy the GPL and LGPL
license files into the generated prebuilt packages.
Also add a .gitignore files to get less spew from 'git status'