build: add vppinfra/warnings.h to exported headers list

To allow the use of WARN_ON/OFF macros to selectively disable build
warnings.

Type: fix

Change-Id: Iceb9d28b2b80c373afb51900880c23041be836db
Signed-off-by: Benoît Ganne <bganne@cisco.com>
diff --git a/src/vppinfra/CMakeLists.txt b/src/vppinfra/CMakeLists.txt
index e667eb0..a10f335 100644
--- a/src/vppinfra/CMakeLists.txt
+++ b/src/vppinfra/CMakeLists.txt
@@ -174,6 +174,7 @@
   vector.h
   vector_neon.h
   vector_sse42.h
+  warnings.h
   xxhash.h
   linux/syscall.h
   linux/sysfs.h