Replace the crufty build-time configure checks for program paths with
equivalent runtime logic.
This lets users install graphing tools as needed without having to reconfigure
and rebuild LLVM, while eliminating a long chain of inappropriate compile
dependencies that included GUI programs and the windowing system.
Additional features:
* Support the OS X 'open' command to view graphs generated by any of the
Graphviz utilities. This is an alternative to the Graphviz OS X UI which is
no longer available on Mountain Lion.
* Produce informative log output upon failure to indicate which programs can
be installed to view graphs.
Ping me if this doesn't work for your particular environment.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210001 91177308-0d34-0410-b5e6-96231b3b80d8
04de60e28f