Move timegm implementation out of Taskwarrior into libshared

CMakeLists.txt

@@ -22,6 +22,7 @@ set (PACKAGE_VERSION "${VERSION}")
 set (PACKAGE_STRING "${PACKAGE} ${VERSION}")
 
 check_function_exists(strlcpy HAVE_STRLCPY)
+check_function_exists(timegm  HAVE_TIMEGM)
 
 message ("-- Configuring cmake.h")
 configure_file (

cmake.h.in

@@ -33,8 +33,10 @@
 /* Found strlcpy() */
 #cmakedefine HAVE_STRLCPY
 
+/* Found timegm(struct tm*) */
+#cmakedefine HAVE_TIMEGM
+
 /* Functions */
 #cmakedefine HAVE_GET_CURRENT_DIR_NAME
-#cmakedefine HAVE_TIMEGM
 #cmakedefine HAVE_UUID_UNPARSE_LOWER
 

src/Datetime.cpp

@@ -3119,6 +3119,23 @@ bool Datetime::validate ()
   return true;
 }
 
+#ifndef HAVE_TIMEGM
+time_t Datetime::timegm(struct tm* tm) {
+  time_t ret;
+  char* tz;
+  tz = getenv("TZ");
+  setenv("TZ", "UTC", 1);
+  tzset();
+  ret = mktime(tm);
+  if (tz)
+    setenv("TZ", tz, 1);
+  else
+    unsetenv("TZ");
+  tzset();
+  return ret;
+}
+#endif
+
 ////////////////////////////////////////////////////////////////////////////////
 // int tm_sec;       seconds (0 - 60)
 // int tm_min;       minutes (0 - 59)

src/Datetime.h

@@ -201,6 +201,10 @@ class Datetime
   bool validate ();
   void resolve ();
 
+  #ifndef HAVE_TIMEGM
+  time_t timegm(struct tm*);
+  #endif
+
 public:
   int _year    {0};
   int _month   {0};