[objc] If we don't know for sure what the designated initializers of the superclass are,
assume that a [super init..] inside a designated initializer also refers to a designated one
and do not warn.
Object/COFF: ExportAddressTableEntry is a union of two RVAs.

The previous definition was wrong. See Microsoft PE/COFF specification
section 5.3.2.
Change stack probing code for MingW.

Since gcc 4.6 the compiler uses ___chkstk_ms which has the same semantics as the
MS CRT function __chkstk. This simplifies the prologue generation a bit.

Reviewed by Rafael Espíndola.