Fix Debian CI Jerboa prefix

ober

3a041a41ea6041c6115a9a5d5e4578828b427cdf

diff --git a/.build.yml b/.build.yml
index 476e378..e41bdda 100644
--- a/.build.yml
+++ b/.build.yml
@@ -34,9 +34,11 @@ tasks:
       test "$(git -C "$HOME/jerboa" rev-parse 'HEAD^{tree}')" = "$JERBOA_TREE"
   - build-jerboa-tools: |
       # Build the current multicall tool so CI exercises the same
-      # jerboa/jerbuild/jpkg image users install.
+      # jerboa/jerbuild/jpkg image users install. An explicit native prefix
+      # prevents the pinned builder's Termux fallback from classifying Debian
+      # as Android and adding -liconv.
       cd jerboa
-      make jerboa
+      PREFIX=/usr make jerboa
       echo 'export PATH="$HOME/jerboa/dist:$PATH"' >> ~/.buildenv
   - package-code: |
       cd jerboa-code