Add std::os::self_exe_name()
Follow symlinks in sysroot

Before this commit, rustc looked in `dirname $0`/../lib for libraries
but that doesn't work when rustc is invoked through a symlink.

This commit makes rustc look in `dirname $(readlink $0)`/../lib, i.e.
it first canonicalizes the symlink before walking up the directory tree.

Fixes #3632.
Make check-summary.py support file globbing

Fixes the following error when executing `make check-lite`:

    Traceback (most recent call last):
      File "/home/bnoordhuis/src/rust/src/etc/check-summary.py", line 27, in <module>
        map(summarise, logfiles)
      File "/home/bnoordhuis/src/rust/src/etc/check-summary.py", line 10, in summarise
        with open(fname) as fd:
    IOError: [Errno 2] No such file or directory: 'tmp/*.log'
auto merge of #11750 : bnoordhuis/rust/follow-rustc-symlink, r=thestinger

Before this commit, rustc looked in `dirname $0`/../lib for libraries
but that doesn't work when rustc is invoked through a symlink.

This commit makes rustc look in `dirname $(readlink $0)`/../lib, i.e.
it first canonicalizes the symlink before walking up the directory tree.

Fixes #3632.