Don't error out on deprecated declaration warnings

The function `unsigned char *MD5(const unsigned char *d, size_t n,
unsigned char *md)` from OpenSSL is deprecated and therefore generates
lots of warnings in the build when compiling against OpenSSL 3.0.

Do not treat these warnings as errors, but keep the warning active. This
should be reverted once OpenSSL-3.0 support arrives.

.github/workflows/build.yml

@@ -23,4 +23,6 @@ jobs:
         run: ./configure --enable-alarm --enable-ansi_color --enable-color --enable-cookie --enable-external_uri_loader --enable-gopher --enable-image --enable-ipv6 --enable-m17n --enable-menu --enable-mouse --enable-nls --enable-nntp --enable-sslverify --enable-unicode --enable-w3mmailer --with-imagelib=imlib2 --with-migemo="cmigemo -q -d /usr/share/cmigemo/utf-8/migemo-dict" --with-ssl --with-gc
 
       - name: build
-        run: OPTS='-Wno-unused-result -Werror' make
+        # TODO(rkta): Remove -Wno-error=deprecated-declarations once support for
+        # OpenSSL 3.0 has arrived.
+        run: make OPTS='-Werror -Wno-error=deprecated-declarations -Wno-unused-result'