Fix make run: add vterm_shim.so dependency, build it if missing

ober

c1e68d79374e36a249e9c8b5550e3950d0ca74a0

diff --git a/Makefile b/Makefile
index 3277736..0b0015a 100644
--- a/Makefile
+++ b/Makefile
@@ -83,7 +83,7 @@ build:
 rebuild:
 	$(JERBUILD) src/ lib/ --force
 
-run: build
+run: build vterm_shim.$(SHLIB_EXT)
 	$(SCHEME) $(LIBDIRS) --script main.ss
 
 repl_shim.$(SHLIB_EXT): support/repl_shim.c