* src/compiler/main.lisp:
   * Add *FILE-COMMENT-FROM-GIT* to control whether to use git to
     derive the file-comment.  Default is T.  Otherwise, the actual
     file-comment is used.
   * Update PROCESS-FILE-COMMENT to use *FILE-COMMENT-FROM-GIT*.

 * bin/build-all.sh
 * bin/build.sh
 * bin/build-world.sh
   * Add -G option to control whether file-comment's are derived from
     git.

I almost always build with sparc_sunc so make it the default.
I only do sparc_gcc for testing that the build still works with gcc.

Just use plain describe, which is close enough.

This isn't needed since we no longer set CC in the Config files.

 bin/build.sh::
 * Revert change that added -M

 bin/rebuild-lisp.sh::
 * Remove the -M option, but leave in the getops and usage changes so
   we get a little command help if needed.

Use getopts to parse the options and also print slightly better error
messages.

 bin/build-utils.sh::
 * asdf is not part of build-utils.sh

 bin/build.sh::
 * Build asdf as part of the normal build because it's always part of
   the main tarball, not the extras tarball.

If the version is not specified, determine a default version based on
the git hash returned by git describe.  Thus, for tagged snapshot
builds, the version will automatically be chosen from the tag, with
"snapshot-" removed.

bootfiles/20d/boot-2012-12-1.lisp::
  Add :alien-callback to *features*

bin/build.sh::
  Change bootstrap directory to 20d.

code/lispinit.lisp::
  * Register :alien-callback feature if enabled.
  * Heap overflow checking depends on gencgc, so register that only if
    both are enabled.

tools/comcom.lisp::
  Compile c-callback only if :alien-callback is a feature.

tools/worldcom.lisp:
  Compile alien-callback onlf if :alien-callback is a feature.

complains about this.)

default version instead of adding the date to it. The tag has most of
the desired information already, and this helps to keep
lisp-implementation-version from having duplicate information.

distribution.

not given, use some reasonable default so we don't end up with a weird
tarball.

make-src-dist.sh to bin.