build: add vppinfra/warnings.h to exported headers list
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 <38aad8ffcfa407b890d258e568f161530f66882d@cisco.com>

chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp