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.

Index: libc/misc/time/time.c

===================================================================

--- a/libc/misc/time/time.c	(revision 17534)

+++ b/libc/misc/time/time.c	(revision 17647)

@@ -158,7 +158,9 @@

 #endif

 #if defined (L_tzset) || defined (L_localtime_r) || defined(L_strftime) || \

-    defined(L__time_mktime) || defined(L__time_mktime_tzi)

+	 defined(L__time_mktime) || defined(L__time_mktime_tzi) || \

+	 ((defined(L_strftime) || defined(L_strftime_l)) && \

+	  defined(__UCLIBC_HAS_XLOCALE__))

 void _time_tzset (int);