[MS] Fix for bug 25013 - #pragma vtordisp is unknown inside functions, by Denis Zobnin.

This patch adds support of #pragma vtordisp inside functions in attempt to improve compatibility. Microsoft compiler appears to save the stack of vtordisp modes on entry of struct methods' bodies and restore it on exit (method-local vtordisp).
Differential Revision: http://reviews.llvm.org/D14467

llvm-svn: 253650