Rename sub-Makefiles into build.mk

So now it is impossible to accidentally start from the wrong place,
and this structure also implicitly tells you how to build

1 files changed, 4 insertions, 0 deletions

diff --git a/src/tool/build.mk b/src/tool/build.mk
new file mode 100644
index 00000000..a60eceee
--- /dev/null
+++ b/src/tool/build.mk
@@ -0,0 +1,4 @@
+OBJS.tool += src/tool/tool.o
+
+src/tool/libngtool.a: ${OBJS.tool}
+	ar rcs src/tool/libngtool.a ${OBJS.tool}