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/Unix/AssertionHandler.cpp

@@ -2,7 +2,9 @@
 #include "RageUtil.h"
 #include "RageException.h"
 #include "archutils/Unix/EmergencyShutdown.h"
+#if defined(HAVE_UNISTD_H)
 #include <unistd.h>
+#endif
 #include <assert.h>
 
 /* We can define this symbol to catch failed assert() calls.  This is only used

src/archutils/Unix/Backtrace.cpp

@@ -2,13 +2,17 @@
 #include "Backtrace.h"
 #include "RageUtil.h"
 
+#if defined(HAVE_UNISTD_H)
 #include <unistd.h>
+#endif
 #include <cstdlib>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <sys/stat.h>
 #include <cerrno>
+#if defined(HAVE_FCNTL_H)
 #include <fcntl.h>
+#endif
 
 #if defined(BACKTRACE_METHOD_X86_LINUX)
 #include "archutils/Common/PthreadHelpers.h"

src/archutils/Unix/BacktraceNames.cpp

@@ -6,7 +6,9 @@
 #include <cstdio>
 #include <cstdlib>
 #include <cstdarg>
+#if defined(HAVE_UNISTD_H)
 #include <unistd.h>
+#endif
 #include <cstring>
 #include <cerrno>
 

src/archutils/Unix/CrashHandler.cpp

@@ -3,10 +3,14 @@
 #include <cstdio>
 #include <cstdlib>
 #include <cstdarg>
+#if defined(HAVE_UNISTD_H)
 #include <unistd.h>
+#endif
 #include <cerrno>
 #include <limits.h>
+#if defined(HAVE_FCNTL_H)
 #include <fcntl.h>
+#endif
 #include <csignal>
 
 #include "RageLog.h" /* for RageLog::GetAdditionalLog, etc, only */

src/archutils/Unix/GetSysInfo.cpp

@@ -1,7 +1,9 @@
 #include "global.h"
 #include "GetSysInfo.h"
 
+#if defined(HAVE_SYS_UTSNAME_H)
 #include <sys/utsname.h>
+#endif
 
 void GetKernel( RString &sys, int &iVersion )
 {

src/archutils/Unix/SignalHandler.cpp

@@ -8,7 +8,9 @@
 #include "archutils/Common/PthreadHelpers.h"
 #endif
 
+#if defined(HAVE_UNISTD_H)
 #include <unistd.h>
+#endif
 #include <sys/mman.h>
 #include <cerrno>
 

src/archutils/Unix/arch_setup.h

@@ -9,7 +9,7 @@
 #include <alloca.h>
 #endif
 
-#if !defined(MISSING_STDINT_H) /* need to define int64_t if so */
+#if defined(HAVE_STDINT_H) /* need to define int64_t if so */
 #include <stdint.h>
 #endif
 
@@ -19,13 +19,7 @@
 #ifdef BSD
 #undef ALIGN
 #undef MACHINE
-#if defined(__NetBSD_Version__) && __NetBSD_Version__ < 299000900
-#define lrintf(x) ((int)rint(x))
 #endif
-#endif
-
-/* For RageLog */
-#define HAVE_VERSION_INFO
 
 #include "archutils/Common/gcc_byte_swaps.h"