Enable reading of Dwarf2 frame-unwind info on MacOS.  It seems
as if more recent XCodes rely on it.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14660 a5019735-40e9-0310-863c-91ae7b9d1cf9
Darwin only: add a filter mechanism that aims to remove pointless
memory-map resync operations.  Without the filter, such operations
come to dominate the running time of complex apps with thousands of
memory segments (eg Firefox) and it becomes unusably slow.  With
the filter in place, the huge performance loss is mostly avoided.

Has no meaning and no effect on non-Darwin targets.  Controlled by
flag --resync-filter=no|yes|verbose [yes].  Filter is currently only
set up for Mac OS X 10.9 (Mavericks) 64 bit and will not produce
any performance benefit on any other configuration.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14661 a5019735-40e9-0310-863c-91ae7b9d1cf9