[StatepointLowering] Remove distinction between call and invoke safepoints

There is no point in having invoke safepoints handled differently than the
call safepoints. All relevant decisions could be made by looking at whether
or not gc.result and gc.relocate lay in a same basic block. This change will
 allow to lower call safepoints with relocates and results in a different 
basic blocks. See test case for example.

Differential Revision: http://reviews.llvm.org/D14158

llvm-svn: 252028