[build] Reduce scope of wildcard .gitignore rules

Ensure that .gitignore rules do not cover any files that do exist
within the repository.

Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
diff --git a/src/.gitignore b/src/.gitignore
index cc8e33e..4e4f00c 100644
--- a/src/.gitignore
+++ b/src/.gitignore
@@ -1,4 +1,4 @@
 .toolcheck
 .echocheck
 TAGS*
-bin*
+bin-*