[Bug other/91879] --with-build-sysroot doesn't work as expected

[stsp at users dot sourceforge.net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91879

--- Comment #16 from Stas Sergeev <stsp at users dot sourceforge.net> ---
(In reply to Jonathan Wakely from comment #15)
> For the record, this has moved to
> https://gcc.gnu.org/ml/gcc-help/2019-10/msg00002.html

Thanks, I also would like to apologize to Joseph for
not following his suggestion and instead keeping to
fight with the gcc build system. I can't help feeling
there is a bug here, and I think I am quite close to
getting it solved, so I'd be upset having to change the
approach after so many investigations, at least for now.

I've found this patch of Paolo Bonzini:
https://gcc.gnu.org/ml/gcc-patches/2006-01/msg00823.html
---
        (GCC_TARGET_TOOL): Do not use a host tool if we found a target tool
        with a complete path in either $with_build_time_tools or $exec_prefix.
---

That made me think that --with-build-time-tools=
should override the in-tree tools, but it is
not what actually happens. More details here:
https://gcc.gnu.org/ml/gcc-help/2019-10/msg00002.html
Basically, the idea was to build one djgpp on host,
and then use that one for building the target libs
in another build tree. But it doesn't pick up the
host-installed tools.
After looking at the Paolo's patch, I tried the following
change:

--- config/acx.m4.old  2019-10-02 02:39:31.976773572 +0300
+++ config/acx.m4      2019-10-02 02:08:57.223563920 +0300
@@ -522,7 +522,7 @@
   fi
 else
   ifelse([$4],,,
-  [ok=yes
+  [ok=no
   case " ${configdirs} " in
     *" patsubst([$4], [/.*], []) "*) ;;
     *) ok=no ;;


And indeed got the build done, as --with-build-time-tools=
now found all the host tools in preference of the in-tree tools.
So currently I suspect Paolo's patch is at fault.