[libvirt] with these, clang vs. libvirt reports no errors

I've been running clang regularly, and there have been a few pesky false-positives that just won't go away. It's not productive to reexamine them each time, so I've wanted a way to educate clang without polluting the code with work-arounds that we'll be stuck maintaining and asking questions about long after clang becomes smart enough that those work-arounds are no longer required. My solution is to mark the work-arounds with a new macro, sa_assert (for "static analysis assert"), which acts just like the classical "assert", but is only enabled when compiled by a static analyzer like clang or coverity. The advantage of using an assert-like macro is that people already know that it must have no side-effects and that will make it easy to remove later, when clang grows up. One question you may ask is why add a new symbol, when "assert" itself can already do this via NDEBUG (defined, any assertions are disabled, not defined, they are enabled). There are a few assertions in the code now, and I prefer not to touch them, and to make it clear that these are helping us cater to static analyzers. [PATCH 1/7] sa_assert: new assert-like macro, enabled only for use with static analyzers [PATCH 2/7] build: set STATIC_ANALYSIS when running via clang or coverity [PATCH 3/7] nwfilter_ebiptables_driver.c: avoid NULL dereference [PATCH 4/7] virGetHostnameLocalhost: avoid FP NULL-ptr-deref from clang [PATCH 5/7] qemudDomainAttachSCSIDisk: avoid FP NULL-ptr-deref from clang [PATCH 6/7] xend_internal.c: assure clang that we do not dereference NULL [PATCH 7/7] qemudDomainAttachSCSIDisk: avoid FP NULL-ptr-deref from clang