BUILD: Remove nowarn for warnings that do not trigger

Tested with

    make -j4 all TARGET=linux-glibc USE_OPENSSL=1 USE_LUA=1 USE_ZLIB=1 USE_PCRE2=1 USE_PCRE2_JIT=1 USE_GETADDRINFO=1

against

    gcc (Debian 9.3.0-13) 9.3.0
    Copyright (C) 2019 Free Software Foundation, Inc.
    This is free software; see the source for copying conditions.  There is NO
    warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
1 file changed