Change jerry_port interface to allow for a correct implementation of timezones. (#2540)

The previous jerry_port interface did not allow timezones to be handled correctly,
even if the host system was up to the task. This PR changes the jerry_port interface
to allow a completely correct implementation to exist, and provides one (for Linux/BSD
systems) in default-date.c.

Fixes #1661

JerryScript-DCO-1.0-Signed-off-by: crazy2be crazy1be@gmail.com

jerry-port/default/CMakeLists.txt

@@ -26,6 +26,19 @@ file(GLOB SOURCE_PORT_DEFAULT *.c)
 # (should only be necessary if we used compiler default libc but not checking that)
 set(DEFINES_PORT_DEFAULT _BSD_SOURCE _DEFAULT_SOURCE)
 
+INCLUDE (CheckStructHasMember)
+# CHECK_STRUCT_HAS_MEMBER works by trying to compile some C code that accesses the
+# given field of the given struct. However, our default compiler options break this
+# C code, so turn a couple of them off for this.
+set(CMAKE_REQUIRED_FLAGS "-Wno-error=strict-prototypes -Wno-error=old-style-definition")
+# tm.tm_gmtoff is non-standard, so glibc doesn't expose it in c99 mode
+# (our default). Define some macros to expose it anyway.
+set(CMAKE_REQUIRED_DEFINITIONS "-D_BSD_SOURCE -D_DEFAULT_SOURCE")
+CHECK_STRUCT_HAS_MEMBER ("struct tm" tm_gmtoff time.h HAVE_TM_GMTOFF)
+if(HAVE_TM_GMTOFF)
+  set(DEFINES_PORT_DEFAULT ${DEFINES_PORT_DEFAULT} HAVE_TM_GMTOFF)
+endif()
+
 # Sleep function availability check
 INCLUDE (CheckIncludeFiles)
 CHECK_INCLUDE_FILES (time.h HAVE_TIME_H)