The commit <c5b2bc1268> made the warnings below
in the case of OpenSSL 1.1 where the `OPENSSL_FIPS` macro is not defined.
```
$ bundle install --standalone
$ bundle exec rake compile -- \
--with-openssl-dir=$HOME/.local/openssl-1.1.1t-debug \
--with-cflags="-Wundef"
mkdir -p tmp/x86_64-linux/openssl/3.2.1
cd tmp/x86_64-linux/openssl/3.2.1
/usr/local/ruby-3.2.1/bin/ruby -I. -r.rake-compiler-siteconf.rb ../../../../ext/openssl/extconf.rb -- --with-openssl-dir=/home/jaruga/.local/openssl-1.1.1t-debug --with-cflags=-Wundef
...
gcc -I. -I/usr/local/ruby-3.2.1/include/ruby-3.2.0/x86_64-linux -I/usr/local/ruby-3.2.1/include/ruby-3.2.0/ruby/backward -I/usr/local/ruby-3.2.1/include/ruby-3.2.0 -I../../../../ext/openssl -DRUBY_EXTCONF_H=\"extconf.h\" -I/home/jaruga/.local/openssl-1.1.1t-debug/include -fPIC -Wundef -o ossl.o -c ../../../../ext/openssl/ossl.c
../../../../ext/openssl/ossl.c: In function ‘ossl_fips_mode_get’:
../../../../ext/openssl/ossl.c:425:7: warning: "OPENSSL_FIPS" is not defined, evaluates to 0 [-Wundef]
425 | #elif OPENSSL_FIPS
| ^~~~~~~~~~~~
../../../../ext/openssl/ossl.c: In function ‘ossl_fips_mode_set’:
../../../../ext/openssl/ossl.c:460:7: warning: "OPENSSL_FIPS" is not defined, evaluates to 0 [-Wundef]
460 | #elif OPENSSL_FIPS
| ^~~~~~~~~~~~
../../../../ext/openssl/ossl.c: In function ‘Init_openssl’:
../../../../ext/openssl/ossl.c:1218:7: warning: "OPENSSL_FIPS" is not defined, evaluates to 0 [-Wundef]
1218 | #elif OPENSSL_FIPS
| ^~~~~~~~~~~~
...
cp tmp/x86_64-linux/openssl/3.2.1/openssl.so tmp/x86_64-linux/stage/lib/openssl.so
```
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