crypto/x509: update __MAC_OS_X_VERSION_MAX_ALLOWED on Mac
crypto/x509: update __MAC_OS_X_VERSION_MAX_ALLOWED on Mac

Reportedly, -mmacosx-version-min=10.6 -D__MAC_OS_X_VERSION_MAX_ALLOWED=1060
is problematic.

It means min 10.6 and max 10.6, thus exactly 10.6. But we only support
10.8+.

It never caused us problems, because we build on Macs, but apparently
if you cross-compile from Linux with some Mac compiler SDK thing, then
things break?

This was added in https://golang.org/cl/5700083 for #3131, and the
intent at the time was to pin to exactly 10.6. So it wasn't a mistake,
but it is definitely outdated.

Given that we now support 10.8 as the min, update it to 1080.

Fixes #17732

Change-Id: I6cc8ab6ac62b8638a5025952b830f23e8822b2a6
Reviewed-on: https://go-review.googlesource.com/32580
Reviewed-by: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Quentin Smith <d6b8e48afb2534b213e391cab43016505747a234@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

derekmarcotte/go,CAFxX/go,derekmarcotte/go,ImJasonH/go,ImJasonH/go,suncycheng/go,polyverse-security/go,Cofyc/go,codestation/go,vsekhar/elastic-go,suncycheng/go,vsekhar/elastic-go,cloudflare/go,derekmarcotte/go,nawawi/go,goodlang/good,vsekhar/elastic-go,CAFxX/go,akutz/go,Cofyc/go,Cofyc/go,golang/go,golang/go,derekmarcotte/go,codestation/go,josharian/go,suncycheng/go,suncycheng/go,linux-on-ibm-z/go,codestation/go,cloudflare/go,nawawi/go,ImJasonH/go,derekmarcotte/go,CAFxX/go,nawawi/go,derekmarcotte/go,cloudflare/go,linux-on-ibm-z/go,vsekhar/elastic-go,suncycheng/go,goodlang/good,CAFxX/go,ImJasonH/go,derekmarcotte/go,goodlang/good,josharian/go,akutz/go,polyverse-security/go,cloudflare/go,polyverse-security/go,akutz/go,goodlang/good,josharian/go,nawawi/go,goodlang/good,cloudflare/go,josharian/go,Cofyc/go,josharian/go,golang/go,CAFxX/go,vsekhar/elastic-go,CAFxX/go,linux-on-ibm-z/go,codestation/go,akutz/go,ImJasonH/go,Cofyc/go,linux-on-ibm-z/go,ImJasonH/go,suncycheng/go,golang/go,akutz/go,linux-on-ibm-z/go,Cofyc/go,CAFxX/go,Cofyc/go,codestation/go,CAFxX/go,akutz/go,golang/go,goodlang/good,ImJasonH/go,linux-on-ibm-z/go,vsekhar/elastic-go,vsekhar/elastic-go,derekmarcotte/go,cloudflare/go,josharian/go,goodlang/good,goodlang/good,polyverse-security/go,codestation/go,polyverse-security/go,nawawi/go,polyverse-security/go,codestation/go,nawawi/go,codestation/go,josharian/go,linux-on-ibm-z/go,vsekhar/elastic-go,akutz/go,polyverse-security/go,golang/go,golang/go,suncycheng/go,cloudflare/go,christopher-henderson/Go,josharian/go,nawawi/go,cloudflare/go,golang/go,suncycheng/go,akutz/go,polyverse-security/go,ImJasonH/go,nawawi/go,linux-on-ibm-z/go,Cofyc/go