Ah! I finally have a progress bar that doesn't stall the build!
- pipe size in Linux is only 8*512=4096 bytes
- pipe size is not setable
- when the feeding process spits out data faster than the eating
process can read it, then the feeding process stalls after 4KiB
of data sent to the pipe
- for us, the progress bar would spawn a sub-shell every line,
and the sub-shell would in turn spawn a 'date' command.
Which was sloooww as hell, and would cause some kind of a
starvation: the pipe was full most of the time, and the
feeding process was stalled all this time.

Now, we use internal variables and a little hack based onan offset
to determine the elapsed time. Much faster this way, but still
CPU-intensive.

 --- gcc-4.1.2.orig/boehm-gc/include/gc.h	2005-01-02 04:35:57.000000000 +0100

 +++ gcc-4.1.2/boehm-gc/include/gc.h	2007-03-04 23:33:07.000000000 +0100

 @@ -500,7 +500,7 @@

  #ifdef __linux__

  # include <features.h>

  # if (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 1 || __GLIBC__ > 2) \

 -     && !defined(__ia64__)

 +     && !defined(__ia64__) && !defined(__UCLIBC__)

  #   ifndef GC_HAVE_BUILTIN_BACKTRACE

  #     define GC_HAVE_BUILTIN_BACKTRACE

  #   endif