Cmake refresh

Use target objects everywhere, and simplify handling of system vs
local dependencies.

CMakeModules/CheckPOSIXFeatures.cmake

@@ -0,0 +1,50 @@
+check_function_exists(gettimeofday HAVE_GETTIMEOFDAY)
+check_function_exists(rint HAVE_RINT)
+check_function_exists(mkdtemp HAVE_MKDTEMP)
+check_function_exists(bcopy HAVE_BCOPY)
+check_function_exists(mmap HAVE_MMAP)
+
+if (NOT MSVC)
+  check_function_exists(timegm HAVE_TIMEGM)
+  if (NOT HAVE_TIMEGM)
+    message(FATAL_ERROR "Non-Windows platforms must support timegm()")
+  endif()
+endif()
+
+if(HAVE_UNISTD_H)
+    set(CMAKE_REQUIRED_INCLUDES ${CMAKE_INCLUDE_PATH})
+    check_cxx_source_compiles(
+       "#include <unistd.h>
+        #if !defined(_POSIX_TIMERS) || (0 >= _POSIX_TIMERS)
+            #error clock_gettime is not supported
+        #endif
+
+        int main() { return 0; }
+        "
+        HAVE_CLOCK_GETTIME)
+endif(HAVE_UNISTD_H)
+
+set(RT_LIBRARY "")
+if(HAVE_CLOCK_GETTIME)
+    check_library_exists(rt clock_gettime "" HAVE_RT)
+    if(HAVE_RT)
+        set(RT_LIBRARY rt)
+    endif(HAVE_RT)
+endif(HAVE_CLOCK_GETTIME)
+
+set(DL_LIBRARY "")
+check_cxx_source_compiles(
+    "#include <dlfcn.h>
+    int main(void) {
+        return 0;
+    }
+    "
+    HAVE_DLFCN_H)
+
+if(HAVE_DLFCN_H)
+    check_library_exists(dl dlerror "" HAVE_DL)
+    if(HAVE_DL)
+        set(DL_LIBRARY "dl")
+    endif()
+endif()
+