run one test

[DJ Delorie]

One of the small items that was mentioned at Cauldron was "how do to
re-run just one test?"

While it can be done with a suitable command line make invocation,
this is a lot easier...

I'll turn it into a real patch once we bikeshed the target name ;-)

diff --git a/Makefile b/Makefile
index 67ddd01bfe..c424d9ee02 100644
--- a/Makefile
+++ b/Makefile
@@ -499,3 +499,11 @@ FORCE:
 
 iconvdata/% localedata/% po/%: FORCE
 	$(MAKE) $(PARALLELMFLAGS) -C $(@D) $(@F)
+
+# Convenience target to rerun one test, from the top of the build tree
+# Example: make onetest t=wcsmbs/test-wcsnlen
+onetest :
+	@-rm -f $(objpfx)$t.out
+	$(MAKE) subdir=$(dir $t) -C $(dir $t) ..=../ $(objpfx)$t.out
+	@cat $(objpfx)$t.test-result
+	@cat $(objpfx)$t.out