editors/abiword: unbreak build with Clang 6 (C++14 by default)

xap_Dialog.cpp:270:17: error: cast from pointer to smaller type 'char' loses information

*pWindowName = (char) NULL;
               ^~~~~~~~~~~

ap_UnixApp.cpp:866:29: error: invalid suffix on literal; C++11 requires a space between literal and identifier [-Wreserved-user-defined-literal]

if(0 == strcmp (suffix, "."G_MODULE_SUFFIX))
                           ^

ie_exp_XSL-FO.cpp:1454:13: error: invalid suffix on literal; C++11 requires a space between literal and identifier [-Wreserved-user-defined-literal]

buf += " "x"=\""; \
          ^

ie_exp_LaTeX.cpp:1332:43: error: invalid suffix on literal; C++11 requires a space between literal and identifier [-Wreserved-user-defined-literal]
#define SUB(a,who) case a: subst = "\\(\\"who"\\)"; return true;

^

RealmProtocol.cpp:16:2: error: constant expression evaluates to -1 which cannot be narrowed to type 'uint32_t' (aka 'unsigned int') [-Wc++11-narrowing]

RPV1_PACKET_VARIABLE, /* user joined */
^~~~~~~~~~~~~~~~~~~~

RealmProtocol.cpp:10:30: note: expanded from macro 'RPV1_PACKET_VARIABLE'
#define RPV1_PACKET_VARIABLE -1

^~

RealmProtocol.cpp:16:2: note: insert an explicit cast to silence this issue

RPV1_PACKET_VARIABLE, /* user joined */
^~~~~~~~~~~~~~~~~~~~
static_cast<uint32_t>( )

RealmProtocol.cpp:10:30: note: expanded from macro 'RPV1_PACKET_VARIABLE'
#define RPV1_PACKET_VARIABLE -1

^~

soa_soup.cpp:166:11: error: no viable conversion from returned value of type 'soa::GenericPtr' (aka 'shared_ptr<soa::Generic>') to function return type 'bool'

return soa::GenericPtr();
       ^~~~~~~~~~~~~~~~~

Reported by: antoine (via bug 224669)
Obtained from: upstream (partially)