fix MarkLocalAndGlobalVariables descending into intrinsic invocations.
fix webgl class after adding initialization
enable the GC (with finalization) on ios.
sigh, opt flags are still breaking the ios demo.
don't crash if we have spew turned on and page is null
add DebugInfo subclasses, MDNode, MDString, and DIBuilder to the party.
throw an error, not a string, so we get a nice stacktrace from node.
add debug info generation to the compiler.

This change adds a -g flag to the ejs script, which turns out debug mode and turns off optimizations
(we don't even run opt in that case.)

The debuginfo metadata shows up in the .ll file but for some reason it's failing verification and
being stripped out by llvm-as.  It also causes some test compilations to fail, so it's definitely
not ready for prime time.

But soon, working stack traces, nice function symbol names, and breakpoints in gdb/lldb.
clean up the .dSYM directories -g generates
fix this again.  we weren't munmapping enough