Add CMake options for easier profiling on Linux

KEEP_LOCAL_SYMBOLS keeps local symbols in .symtab to get better symbols
from with objdump -d.  perf calls out to objdump -d occasionally, and
it's nice to have this Just Work.

KEEP_FRAME_POINTERS sets -fno-omit-frame-pointer, which I'm using with
perf record -g to get callstacks.  perf only does frame pointer walks
because as a sampling profiler it has to fast.

Review URL: https://codereview.appspot.com/7381058

git-svn-id: https://dynamorio.googlecode.com/svn/trunk@1955 49cc7528-f6fd-11dd-9d1a-b59b2e1864b6