Rename src/ecmascript/spidermonkey/util.c to
src/ecmascript/spidermonkey-shared.c and compile it also when
CONFIG_SCRIPTING_SMJS is enabled but CONFIG_ECMASCRIPT_SPIDERMONKEY is
not. Then use its functions from src/scripting/smjs/ too. Move the
corresponding declarations, as well as the inline functions needed by
src/scripting/smjs/, from src/ecmascript/spidermonkey/util.h to
src/ecmascript/spidermonkey-shared.h.
ELinks is nowadays using two JSRuntimes and SpiderMonkey has bugs that
make it crash in such use. To work around them, ELinks will need to
be changed to use only one JSRuntime. I am planning to define and
initialize that JSRuntime in src/ecmascript/spidermonkey-shared.c,
now that it's compiled whenever either of the modules is enabled.
This is a further precaution against reading a pointer from the wrong
type of object. All of the JS_GetPrivate calls were already protected
with JS_InstanceOf checks if assertions are enabled, and many of them
also if assertions are not enabled.
