Created attachment 1748 [details]
claws-mail-3.15.0-fix-no-common.patch

When including the pygtk headers they create some global symbols. See e.g. this in pygtk.h:
#if defined(NO_IMPORT) || defined(NO_IMPORT_PYGTK)
extern struct _PyGtk_FunctionStruct *_PyGtk_API;
#else
struct _PyGtk_FunctionStruct *_PyGtk_API;
#endif

If these headers get included multiple times then the symbol is defined multiple times, which is not strictly correct C. Other files using the same global symbol have to mark it with "extern". pygtk does that if some #define commands are set. claws includes these headers in two files (src/plugins/python/clawsmailmodule.c, src/plugins/python/python-hooks.c).

Now by default gcc is lax with this and will accept duplicate symbols. However it can be turned into a more strict mode with the "-fno-common" flag. To reproduce:

./configure CFLAGS="-O2 -fno-common"; make

It will show an error like this:
.libs/python_la-python-hooks.o:(.bss+0x8): multiple definition of `_PyGObject_API'
.libs/python_la-clawsmailmodule.o:(.bss+0x8): first defined here
.libs/python_la-python-hooks.o:(.bss+0x0): multiple definition of `_PyGtk_API'
.libs/python_la-clawsmailmodule.o:(.bss+0x0): first defined here


To fix this the proper #define commands need to be set in one of the files including the pygtk headers. I have attached a patch to do that in clawsmailmodule.c. Please apply.