Move ifThenElse helpers to code-gen-x64.cpp

Reviewed By: @jasone

Differential Revision: D1424833
Implement zend EG(error_reporting).

Summary: Use a macro and wrapper class to turn lval/rval use of EG(error_reporting)
into calls to setter/getter methods for class RequestInjectionData.
Closes #3126

Reviewed By: @swtaarrs

Differential Revision: D1424013

Pulled By: @fredemmott