CryptoPkg/CrtLibSupport: add secure_getenv() stub function

CryptoPkg/CrtLibSupport: add secure_getenv() stub function

The Fedora distro ships a modified OpenSSL 1.1.0 package stream. One of
their patches calls the secure_getenv() C library function. We already
have a stub for getenv(); it applies trivially to secure_getenv() as well.
Add the secure_getenv() stub so that edk2 can be built with Fedora's
OpenSSL 1.1.0 sources.

Cc: Qin Long <qin.long@intel.com>
Cc: Ting Ye <ting.ye@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Long Qin <qin.long@intel.com>