Localized the one case where main-cocoa.m sends a string through the z-term interface...

Localized the one case where main-cocoa.m sends a string through the z-term interface.  To handle that, adjusted the make rules so main-cocoa.m gets processed by gcc-wrap.  Since automake issued a warning when OBJCCOMPILE was set only in the condition part for Cocoa builds, it is set, along with COMPILE, regardless of whether building the Cocoa version.