delete AvailabilityMacros.h include
don't execute the dtrace pass if we're not running on darwin

Requires opening /usr/lib/libdtrace.dylib, which doesn't exist on linux.
don't use F_NOCACHE unless it exists
use malloc instead of vm_allocate in rebase.cpp
define AR_EFMT1 if it doesn't already exist
don't expose any of the timing interfaces, as they require mach
remove cross-building HACK
stub out getVMInfo
add linux-compat directory
fix Darwin-vs-GNU qsort_r mismatch in macho_relocatable_file.cpp
#include <arpa/inet.h> for standardized byte-swapping macros
fixup linker passes needing standard headers
wrap Darwin-specific sysctl(2) call in defined(__MACH__)
#include <sys/param.h> for various constants in InputFiles.cpp
avoid -Wnarrowing warnings
#include <string.h> for memchr and friends in blob.cpp
include strlcpycat.h where needed
use correct Dl_info name in AddressSpace.cpp
avoid snapshot functionality on non-Darwin platforms
remove const qualifiers on iterator accessors