added ckeck for Icarus Verilog, otherwise the tests are silently stopped

Signed-off-by: Clifford Wolf <clifford@clifford.at>

tests/simple/run-test.sh

@@ -1,3 +1,10 @@
 #!/bin/bash
+
+# check for Icarus Verilog
+if ! which iverilog > /dev/null ; then
+  echo "$0: Error: Icarus Verilog 'iverilog' not found."
+  exit 1
+fi
+
 make -C ../.. || exit 1
 exec bash ../tools/autotest.sh *.v