Implement run buildfile directive

Now we can do:

run echo 'foo = bar'
print $foo

1 files changed, 36 insertions, 0 deletions

diff --git a/tests/directive/run.test b/tests/directive/run.test
new file mode 100644
index 0000000..a6573f2
--- /dev/null
+++ b/tests/directive/run.test
@@ -0,0 +1,36 @@
+# file      : tests/directive/run.test
+# copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
+# license   : MIT; see accompanying LICENSE file
+
+# We are going to run the build system driver so no cross-testing.
+#
+crosstest = false
+
+.include ../common.test
+
+: no-output
+:
+cat <'assert true' >=buildfile;
+$* <"run $0 noop"
+
+: output
+:
+cat <'print foo=bar' >=buildfile;
+$* <<"EOI" >'bar'
+run $0 noop
+print \$foo
+EOI
+
+: bad-exit
+:
+cat <'assert false' >=buildfile;
+$* <"run $0 noop" 2>>EOE != 0
+buildfile:1:1: error: assertion failed
+EOE
+
+: bad-output
+:
+cat <'print run' >=buildfile;
+$* <"run $0 noop" 2>>~%EOE% != 0
+%-:1:5: \(.+ stdout\):1:4: error: executable name expected after run%
+EOE