CryptoPkg: Fix handling of &strcmp function pointers

CryptoPkg: Fix handling of &strcmp function pointers

In a couple of places, OpenSSL code uses the address of the
strcmp() function, and assigns it to another comparator function
pointer.

Unfortunately, this falls foul of the inconsistent function ABI
that we use in EDKII. We '#define strcmp AsciiStrCmp' but AsciiStrCmp
is an EFIAPI function with the Microsoft ABI. And we're assigning its
address to a non-EFIAPI function, which may well have a different ABI.

Fix this by providing an actual strcmp() function in the default ABI.
We already *had* a prototype for it in OpenSslSupport.h, which was
then superseded by the #define strcmp AsciiStrCmp.

Now, OpenSSL code *can* use &strcmp without problems.

Cc: Ting Ye <ting.ye@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Gary Lin <glin@suse.com>
Cc: Ronald Cron <ronald.cron@arm.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Qin Long <qin.long@intel.com>
Reviewed-by: Ting Ye <ting.ye@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Gary Lin <glin@suse.com>