<rdar://problem/10993996>

Added a new makefile target to help us with Apple builds where the installhdrs
will copy the headers for the shared library. Prior to this fix, the install
headers directory would contain the unix style paths to all public header
files ("#include lldb/API/SBDefines.h") instead of the fixed up framework
header paths ("#include <LLDB/SBDefines.h>").

llvm-svn: 152253