test for -defaultlib=libphobos2.so

- followup to issue 13210

- depends on phobos directory layout for setting LD_LIBRARY_PATH

test/runnable/extra-files/test_shared.d

@@ -0,0 +1,3 @@
+void main()
+{
+}

test/runnable/test_shared.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+dir=${RESULTS_DIR}/runnable
+dmddir=${RESULTS_DIR}${SEP}runnable
+output_file=${dir}/test_shared.sh.out
+
+rm -f ${output_file}
+
+if [ ${OS} != "linux" ]; then
+    echo "Skipping shared library test on ${OS}."
+    touch ${output_file}
+    exit 0
+fi
+
+die()
+{
+    cat ${output_file}
+    rm -f ${output_file}
+    exit 1
+}
+
+$DMD -m${MODEL} -of${dmddir}${SEP}test_shared${EXE} -defaultlib=libphobos2.so runnable/extra-files/test_shared.d >> ${output_file}
+if [ $? -ne 0 ]; then die; fi
+
+LD_LIBRARY_PATH=../../phobos/generated/${OS}/release/${MODEL} ./${dmddir}${SEP}test_shared${EXE}
+if [ $? -ne 0 ]; then die; fi