linked libraries are read in the order they appear

so if libmmtk_ruby is linked to but the linker finds no existing
reference to it, then the link will get thrown away

.github/workflows/ubuntu.yml

@@ -137,11 +137,12 @@ jobs:
             -I.ext/include/x86_64-linux \
             -Wl,--verbose,--compress-debug-sections=zlib \
             -Wl,--rpath=$MMTK_BUILD_PATH \
-            -L$(readlink -f $MMTK_BUILD_PATH) -lmmtk_ruby \
+            -L$(readlink -f $MMTK_BUILD_PATH) \
             -fstack-protector-strong \
             -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 \
             -O3 -fno-fast-math -ggdb3 -DBUILDING_SHARED_GC -fPIC \
-            -o /home/runner/ruby_gc/librubygc.mmtk.so $(pwd)/../src/gc/mmtk.c &&
+            -o /home/runner/ruby_gc/librubygc.mmtk.so $(pwd)/../src/gc/mmtk.c \
+            -lmmtk_ruby &&
           ldd ${{ matrix.shared_gc_dir }}/librubygc.mmtk.so
         if: ${{ matrix.shared_gc }}