This flag is used internally by EffectSystem as a sign of compiling
stdlib. If this flag is present, then EffectSystem will read contracts
on functions and serialize them into metadata even if corresponding
LanguageFeatures are turned off. This is done solely for building
1.2-runtime with contracts in it without the need to turn on
LanguageFeatures manually.
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This commit finishes a first series of commits related to effect
system. After it, compiler is ready to work with contracts, but it is
impossible to actually annotate anything, because there are no
contracts DSL in stdlib yet.
Dmitry Savvinov
eae9923dbe