[build_cmake] clock_gettime() -lrt w/ glibc < 2.17 (fixes #2737)

clock_gettime() needs -lrt with glibc < 2.17,
and possibly other platforms

This commit contains fixes for CMake and SCONS
See also commit:4d920466 which updated configure.ac for same

x-ref:
  "1.4.40 compiling issuses on Debian Wheezy"
  https://redmine.lighttpd.net/issues/2737

SConstruct

@@ -210,7 +210,7 @@ if 1:
 			gethostbyname poll epoll_ctl getrlimit chroot \
 			getuid select signal pathconf madvise prctl\
 			writev sigaction sendfile64 send_file kqueue port_create localtime_r posix_fadvise issetugid inet_pton \
-			memset_s explicit_bzero'))
+			memset_s explicit_bzero clock_gettime'))
 
 	checkTypes(autoconf, Split('pid_t size_t off_t'))
 
@@ -232,6 +232,9 @@ if 1:
 	else:
 		checkFuncs(autoconf, ['crypt', 'crypt_r']);
 
+	if autoconf.CheckLibWithHeader('rt', 'time.h', 'c', 'clock_gettime(CLOCK_MONOTONIC, (struct timespec*)0);'):
+		autoconf.env.Append(CPPFLAGS = [ '-DHAVE_CLOCK_GETTIME' ], LIBS = [ 'rt' ])
+
 	if autoconf.CheckLibWithHeader('uuid', 'uuid/uuid.h', 'C'):
 		autoconf.env.Append(CPPFLAGS = [ '-DHAVE_UUID_UUID_H', '-DHAVE_LIBUUID' ], LIBUUID = 'uuid')
 

src/CMakeLists.txt

@@ -1,6 +1,7 @@
 include(CheckCSourceCompiles)
 include(CheckIncludeFiles)
 include(CheckFunctionExists)
+include(CheckSymbolExists)
 include(CheckVariableExists)
 include(CheckTypeSize)
 include(CheckLibraryExists)
@@ -157,6 +158,10 @@ check_function_exists(issetugid HAVE_ISSETUGID)
 check_function_exists(inet_pton HAVE_INET_PTON)
 check_function_exists(memset_s HAVE_MEMSET_S)
 check_function_exists(explicit_bzero HAVE_EXPLICIT_BZERO)
+check_symbol_exists(clock_gettime "time.h" HAVE_CLOCK_GETTIME)
+if (NOT HAVE_CLOCK_GETTIME)
+	check_library_exists(rt clock_gettime "time.h" HAVE_CLOCK_GETTIME)
+endif()
 check_c_source_compiles("
 	#include <sys/types.h>
 	#include <sys/socket.h>