git-compat-util: suppress unavoidable Apple-specific deprecation warnings

With the release of Mac OS X 10.7 in July 2011, Apple deprecated all openssl.h functionality due to OpenSSL ABI (application binary interface) instability, resulting in an explosion of compilation warnings about deprecated SSL, SHA1, and X509 functions (among others). 61067954ce (cache.h: eliminate SHA-1 deprecation warnings on Mac OS X; 2013-05-19) and be4c828b76 (imap-send: eliminate HMAC deprecation warnings on Mac OS X; 2013-05-19) attempted to ameliorate the situation by taking advantage of drop-in replacement functionality provided by Apple's (ABI-stable) CommonCrypto facility, however CommonCrypto supplies only a subset of deprecated OpenSSL functionality, thus a host of warnings remain. Despite this shortcoming, it was hoped that Apple would ultimately provide CommonCrypto replacements for all deprecated OpenSSL functionality, and that the effort started by 61067954ce and be4c828b76 would be continued and eventually eliminate all deprecation warnings. However, now 3.5 years later, and with Mac OS X at 10.10, the hoped-for CommonCrypto replacements have not yet materialized, nor is there any indication that they will be forthcoming. These Apple-specific warnings are pure noise: they don't tell us anything useful and we have no control over them, nor is Apple likely to provide replacements any time soon. Such noise may obscure other legitimate warnings, therefore silence them. Signed-off-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>