Define per-target OSX_ARCHITECTURES property

The CMAKE_OSX_ARCHITECTURES variable works only as a global setting.
This commit defines target properties

  OSX_ARCHITECTURES
  OSX_ARCHITECTURES_<CONFIG>

to specify OS X architectures on a per-target and per-configuration
basis.  See issue #8725.

Source/cmMakefileExecutableTargetGenerator.cxx

@@ -229,6 +229,10 @@ void cmMakefileExecutableTargetGenerator::WriteExecutableRule(bool relink)
   // Add language feature flags.
   this->AddFeatureFlags(flags, linkLanguage);
 
+#ifdef __APPLE__
+  this->LocalGenerator->AddArchitectureFlags(flags, this->Target, linkLanguage, this->ConfigName);
+#endif /* __APPLE__ */
+
   // Add target-specific linker flags.
   this->LocalGenerator->AppendFlags
     (linkFlags, this->Target->GetProperty("LINK_FLAGS"));