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>

CryptoPkg/Library/Include/CrtLibSupport.h

@@ -163,6 +163,7 @@ gid_t          getgid      (void);
 gid_t          getegid     (void);
 void           qsort       (void *, size_t, size_t, int (*)(const void *, const void *));
 char           *getenv     (const char *);
+char           *secure_getenv (const char *);
 #if defined(__GNUC__) && (__GNUC__ >= 2)
 void           abort       (void) __attribute__((__noreturn__));
 #else