Enable two-step allocator on FreeBSD
Currently the two-step allocator is disabled on FreeBSD as the MEM_NORESERVE macro is undefined. It seems that FreeBSD provided this macro until 2014, when it was removed as it wasn't implemented in the kernel. Regardless, Viktor Dukhovni reports empirical evidence on ghc-devs that just plain mmap does what we want.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.4.3 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
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| Blocking | |
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| Operating system | |
| Architecture |