compiler/libec; bootstrap: Improved anonymous instantiations implementation

compiler/libec; bootstrap: Improved anonymous instantiations implementation
- Previously, a global '__ecereTemp%d' variable was used to temporarily hold the instance handle
  This caused problems at least with GCC 4.4.5/64 bit with -O2, where multiple initializers
  used the same variable, e.g. Array { [ Object { }, Object { } ]
- Now using GNU C compound statement expression with an internal declaration to solve this issue