CXX-204 Use vendored timegm implementation if platform does not offer it

(cherry picked from commit 5bf477a)

Conflicts:
	SConstruct
	src/mongo/util/time_support.cpp

Author: acmorrow

SConstruct

@@ -1434,6 +1434,11 @@ def doConfigure(myenv):
         if not conf.CheckLib("execinfo"):
             Exit(1)
 
+    conf.env['MONGO_HAVE_TIMEGM'] = conf.CheckDeclaration(
+        'timegm', includes="#include <time.h>", language='C')
+    if conf.env['MONGO_HAVE_TIMEGM']:
+        conf.env.Append(CPPDEFINES=['MONGO_HAVE_TIMEGM'])
+
     # 'tcmalloc' needs to be the last library linked. Please, add new libraries before this 
     # point.
     if get_option('allocator') == 'tcmalloc':

src/SConscript.client

@@ -107,13 +107,15 @@ clientSourceBasic = [
     'third_party/murmurhash3/MurmurHash3.cpp',
     ]
 
+clientSourceTz = [] if clientEnv['MONGO_HAVE_TIMEGM'] else ['third_party/tz/timegm.c']
+
 clientSourceSasl = [
     'mongo/client/sasl_client_authenticate_impl.cpp',
     'mongo/client/sasl_client_session.cpp',
     'mongo/client/sasl_sspi.cpp',
 ]
 
-clientSourceAll = clientSourceBasic + clientSourceSasl
+clientSourceAll = clientSourceBasic + clientSourceTz + clientSourceSasl
 
 usingSasl = libEnv['MONGO_BUILD_SASL_CLIENT']
 

src/mongo/util/time_support.cpp

@@ -40,6 +40,13 @@
 #define snprintf _snprintf
 #endif
 
+#if !defined(MONGO_HAVE_TIMEGM)
+// Not all systems have timegm defined (it isn't part of POSIX), so fall back to our vendored
+// implementation if our configure checks did not detect it as available on the current
+// system. See SERVER-13446, SERVER-14019, and CXX-204.
+extern "C" time_t timegm(struct tm *const tmp);
+#endif
+
 namespace mongo {
 
     // jsTime_virtual_skew is just for testing. a test command manipulates it.