Almost a complete rewrite of FunctionResolution to now resolve functions

and global variables.

This fixes bug: FuncResolve/2002-08-19-ResolveGlobalVarsEasier.ll
And bug: SingleSource/UnitTests/2002-10-09-ArrayResolution.c

Note that this does not fix bug:
FunctionResolve/2002-08-19-ResolveGlobalVars.ll because replaceAllUsesWith
breaks when a constantexpr is pointing to the thing being replaced.  This
is more of an infrastructure problem than anything.

llvm-svn: 4099