Efl: Add internal strong symbol to fix build on GCC < 5.3

This fixes a crash in ecore_init, calling a weak function from
libefl that was resolved to NULL.

So, here's a fun thing happening with GCC < 5.3. Since a1a506e13e
all EOAPI and EO class_get() functions are weak symbols. This means
that all APIs inside libefl.so are weak.

As a result, gcc linker with --as-needed skipped linking to libefl
since not a single strong symbol from libefl was required by
libecore. This is actually a bug in gcc linker since we do in fact
use symbols from libefl, just weak ones.

GCC 5.3 seems to be fixed, so people with GCC 5.3+ will not
experience any build/runtime issue. The current patch is
a workaround that bug, by artifically creating a strong symbol
required by ecore.

Other libraries than ecore might also need to call
__efl_internal_init, if they end up not being linked to libefl.

src/lib/ecore/ecore.c

@@ -210,6 +210,9 @@ ecore_init(void)
    if (++_ecore_init_count != 1)
      return _ecore_init_count;
 
+   /* make sure libecore is linked to libefl - workaround gcc bug */
+   __efl_internal_init();
+
    setlocale(LC_CTYPE, "");
    /*
       if (strcmp(nl_langinfo(CODESET), "UTF-8"))

src/lib/efl/Efl.h

@@ -119,6 +119,9 @@ typedef Efl_Gfx_Path_Command_Type Efl_Gfx_Path_Command;
 
 #endif
 
+/* work-around bug in gcc --as-needed link optimization */
+EAPI void __efl_internal_init(void);
+
 #if defined ( __cplusplus )
 }
 #endif

src/lib/efl/interfaces/efl_interfaces_main.c

@@ -37,3 +37,9 @@ EAPI const Eo_Event_Description _EFL_GFX_PATH_CHANGED =
 #include "interfaces/efl_animator.eo.c"
 #include "interfaces/efl_orientation.eo.c"
 #include "interfaces/efl_flip.eo.c"
+
+EAPI void
+__efl_internal_init(void)
+{
+   /* nothing to do, the symbol only is required for link to work */
+}