[ruby/openssl] Append flags from environment variables.

According to the `mkmf.rb#init_mkmf`, there are command line options below.

* `--with-cflags` to set the `cflags`
* `--with-ldflags` to set the `ldflags`

For example the following command compiles with the specified flags. Note that
`MAKEFLAGS` is to print the compiler command lines.

```
$ MAKEFLAGS="V=1" \
  bundle exec rake compile -- \
  --with-cflags="-Wundef -Werror" \
  --with-ldflags="-fstack-protector"
```

However, I couldn't find command line options to append the flags. And this
commit is to append the `cflags` and `ldflags` by the environment variables.

```
$ MAKEFLAGS="V=1" \
  RUBY_OPENSSL_EXTCFLAGS="-Wundef -Werror" \
  RUBY_OPENSSL_EXTLDFLAGS="-fstack-protector" \
  bundle exec rake compile
```

https://github.com/ruby/openssl/commit/b551eb86f6

0 files changed, 0 insertions, 0 deletions