vpxenc: Move config check code into its own source files.

- Add command line args that allow display of warnings without prompting
  for user input.
- Extend warning code to make it somewhat scalable.

Change-Id: I2bad8f9315f6eed120c2e1bbe0a2a5ede15fbf35
diff --git a/examples.mk b/examples.mk
index 2600a9d..fe36c4f 100644
--- a/examples.mk
+++ b/examples.mk
@@ -41,6 +41,7 @@
 vpxenc.SRCS                 += ivfdec.c ivfdec.h
 vpxenc.SRCS                 += ivfenc.c ivfenc.h
 vpxenc.SRCS                 += tools_common.c tools_common.h
+vpxenc.SRCS                 += warnings.c warnings.h
 vpxenc.SRCS                 += webmenc.c webmenc.h
 vpxenc.SRCS                 += vpx_ports/mem_ops.h
 vpxenc.SRCS                 += vpx_ports/mem_ops_aligned.h