Such "#ifdef USE_QUIC" prepocessor statements are used by QUIC C header
to avoid inclusion of QUIC headers when the QUIC support is not enabled
(by USE_QUIC make variable). Furthermore, this allows inclusions of QUIC
header from C file without having to protect them with others "#ifdef USE_QUIC"
statements as follows:
So, here if this quic_ssl.h header was included by a C file, and compiled without
QUIC support, this will lead to build errrors as follows:
In file included from <a C file...>:
include/haproxy/quic_ssl.h:35:35: warning: ‘enum ssl_encryption_level_t’
declared inside parameter list will not be visible outside of this
definition or declaration
Should be backported to 2.9 to avoid such building issues to come.