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/BaseCryptLib/SysCall/CrtWrapper.c

@@ -361,6 +361,19 @@ char *getenv (const char *varname)
   return NULL;
 }
 
+/* Get a value from the current environment */
+char *secure_getenv (const char *varname)
+{
+  //
+  // Null secure_getenv() function implementation to satisfy the linker, since
+  // there is no direct functionality logic dependency in present UEFI cases.
+  //
+  // From the secure_getenv() manual: 'just like getenv() except that it
+  // returns NULL in cases where "secure execution" is required'.
+  //
+  return NULL;
+}
+
 //
 // -- Stream I/O Routines --
 //

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