CryptoPkg CLANG35: add -std=c99 to dodge OpenSSL C atomics issue

CryptoPkg CLANG35: add -std=c99 to dodge OpenSSL C atomics issue

Commit c51f8bae7cabe ("CryptoPkg: Fix possible build problem with
Clang") added -std=c99 to the CLANG38 compiler command line of
packages that incorporate parts of OpenSSL, to ensure that the new
C atomics code used by OpenSSL for refcounting (which we don't care
about) does not pull in system C library headers, which we cannot
rely on when (cross)building EDK2 code.

Unsurprisingly, CLANG35 (which is only defined for ARM and AARCH64)
suffers from the exact same issue, so let's add the same flags
there as well.

Reviewed-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>