Circumvent a problem of lacking GetEnvironmentVariable() in WindowsCE.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8596)

(cherry picked from commit 3d098890b23598d1f9455b354f46045a231459cd)