allow global suppression of link flags (#3592)

CRYPTOGRAPHY_SUPPRESS_LINK_FLAGS will now suppress link flags regardless
of platform. Additionally, CRYPTOGRAPHY_WINDOWS_LINK_LEGACY_OPENSSL is
now the flag you need if you want to link against < 1.1.0 on windows.
diff --git a/docs/development/getting-started.rst b/docs/development/getting-started.rst
index 66173d4..0d7c91e 100644
--- a/docs/development/getting-started.rst
+++ b/docs/development/getting-started.rst
@@ -46,7 +46,7 @@
         pip install --requirement ./dev-requirements.txt
 
 Alternatively for a static build you can specify
-``CRYPTOGRAPHY_OSX_NO_LINK_FLAGS=1`` and ensure ``LDFLAGS`` points to the
+``CRYPTOGRAPHY_SUPPRESS_LINK_FLAGS=1`` and ensure ``LDFLAGS`` points to the
 absolute path for the `OpenSSL`_ libraries before calling pip.
 
 .. tip::