Index: apps/build.tcl
===================================================================
diff -u -r831a01f7a3f3ad9a77b87b12c3adac44123507ce -r5a80e290968c4a48ef91cf714f522edb8a75c6d5
--- apps/build.tcl	(.../build.tcl)	(revision 831a01f7a3f3ad9a77b87b12c3adac44123507ce)
+++ apps/build.tcl	(.../build.tcl)	(revision 5a80e290968c4a48ef91cf714f522edb8a75c6d5)
@@ -80,7 +80,14 @@
   
   switch -exact -- $TOOLCHAIN {
     autoconf-tea {
-      exec >@stdout 2>@stderr bash -lc "./configure --libdir=$tclDir --enable-64bit"
+      set opts [list --libdir=$tclDir --enable-64bit]
+
+      # see https://core.tcl-lang.org/tips/doc/trunk/tip/538.md
+      if {$TCLTAG eq "core-8-branch"} {
+        lappend opts "--without-system-libtommath"
+      }
+      
+      exec >@stdout 2>@stderr bash -lc "./configure $opts"
       exec >@stdout 2>@stderr bash -lc "make"
       
       cd $BUILDDIR