Add tests/verilog/local_include.*

`read_verilog` supports checking both the current directory and the source directory for relative includes.  Make sure we aren't regressing that.

tests/verilog/local_include.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+
+set -eu
+
+# only works with read_verilog
+yosys='../../yosys -f verilog'
+test='-p hierarchy'
+subdir=subdir
+source=local_include.v
+include=temp_foo.v
+
+# no include file should fail
+rm -f $include
+echo "logger -expect error $include 1; read_verilog $source" | $yosys
+
+# both files local
+echo 'module foo (input a, output b); assign b = a; endmodule' > $include
+$yosys $test $source
+
+# include local to cwd
+mkdir -p $subdir
+cp -t $subdir $source
+$yosys $test $subdir/$source
+
+# include local to source
+mv -t $subdir $include
+$yosys $test $subdir/$source
+
+# include local to source, and source is given as an absolute path
+$yosys $test $(pwd)/$subdir/$source