Add x64 dbghelp.dll and symsrv.dll paths used by VS2010+
Add x64 dbghelp.dll and symsrv.dll paths used by VS2010+

Review URL: https://codereview.appspot.com/80900044/

SVN-Revision: 1829

LohithBlaze/drmemory,code4bones/drmemory,LohithBlaze/drmemory,code4bones/drmemory,code4bones/drmemory,sigma-random/drmemory,sigma-random/drmemory,sigma-random/drmemory,sigma-random/drmemory,LohithBlaze/drmemory,code4bones/drmemory,code4bones/drmemory,LohithBlaze/drmemory,sigma-random/drmemory,LohithBlaze/drmemory