Use proper cmake detection of features.

This attempts to organize all needed items and places appropriate defines
in a single location. Redundant comparisons/defines were removed when noticed.

A few caveats, however:

* This may be better targeted towards the 5_1_0 branch instead of master right now.
* Cmake will run a little slower on configuration/generation now. That's due to the sanity checks it runs.
* There are some more checks to be added later, but this should be a solid start.

Thanks to the [libical](https://github.com/libical/libical) project for inspiration.

src/archutils/Darwin/Crash.cpp

@@ -4,7 +4,9 @@
 #include "arch/ArchHooks/ArchHooks.h"
 #include <CoreServices/CoreServices.h>
 #include <sys/types.h>
+#if defined(HAVE_UNISTD_H)
 #include <unistd.h>
+#endif
 #include <sys/sysctl.h>
 
 RString CrashHandler::GetLogsDirectory()

src/archutils/Darwin/arch_setup.h

@@ -4,7 +4,6 @@
 // Replace the main function.
 extern "C" int sm_main( int argc, char *argv[] );
 
-#define HAVE_VERSION_INFO
 #define HAVE_CXA_DEMANGLE
 #define HAVE_FFMPEG
 #define HAVE_PTHREAD_COND_TIMEDWAIT
@@ -12,11 +11,6 @@ extern "C" int sm_main( int argc, char *argv[] );
  * this in all cases. If only they could be consistent... */
 #define HAVE_DECL_SIGUSR1 1
 
-/* We have <machine/endian.h> which gets pulled in when we use gcc 4.0's <cstdlib>
- * but no <endian.h>. The definitions of LITTLE_ENDIAN, BIG_ENDIAN and end up conflicting
- * even though they resolve to the same thing (bug in gcc?). */
-#define HAVE_MACHINE_ENDIAN_H
-#define HAVE_INTTYPES_H
 #define __STDC_FORMAT_MACROS
 #define CRASH_HANDLER
 
@@ -25,7 +19,6 @@ extern "C" int sm_main( int argc, char *argv[] );
 #define NO_GL_FLUSH
 
 #define CPU_X86
-#define ENDIAN_LITTLE
 #define BACKTRACE_METHOD_X86_DARWIN
 #define BACKTRACE_LOOKUP_METHOD_DLADDR