Update libvterm to upstream revision 619.

Change-Id: I9a734b40a172d9c13be4fdf38db60c6916d7d8d0
diff --git a/Android.mk b/Android.mk
index 4eeca87..dac5231 100644
--- a/Android.mk
+++ b/Android.mk
@@ -18,6 +18,12 @@
     src/screen.c \
     src/state.c
 
-LOCAL_CFLAGS := -std=c99
+LOCAL_CFLAGS += \
+    -std=c99 \
+    -Wno-missing-field-initializers \
+    -Wno-sign-compare \
+    -Wno-unused-parameter \
+
+LOCAL_CLANG := true
 
 include $(BUILD_STATIC_LIBRARY)