So use the avoid-ATSUI patch dependingh on (the newly added)
MAXOSX_SDK_VERSION, not MAC_OS_X_VERSION_MAX_ALLOWED.

It is not clear (to me at least) whether for instance building against
SDK version 10.7 but with MAC_OS_X_VERSION_MAX_ALLOWED=1060 ensures
the resulting binaries actually work on 10.6. Somebody should
check. If it doesn't work, we should add a check to configure.in that
the min-required and max-allowed values are not less than the SDK
version.

(If it would work even for MAC_OS_X_VERSION_MAX_ALLOWED=1040, we
would not need to require the increasingly obsolete Xcode 3 and 10.4
SDK for "official" builds.)

Change-Id: Ia7088a26024ed288db55fa734465138d44d2ae12