In pkgsStatic, /all/ build inputs are propagated. This means that
netbsd.compat was propagated, along with its setup hook, which broke
static glib builds because glib defines a function with the same name
as one in nbtool_config.h, and nbtool_config.h was being automatically
included in every C file processed by the compiler, in any transitive
dependent of netbsd.compat's setup hook.
To fix this, rather than forcing nbtool_config.h to be included for
_every_ C file in a derivation that depends on netbsd.compat, modify
the NetBSD-specific mkDerivation to detect files that need the header,
and patch it in there where appropriate. That way, only files that
are part of NetBSD will be affected, not all transitive dependents.
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