[Regression] Nim segfaults

[yglukhov]

type NSScreen {.importc, header: "<AppKit/AppKit.h>", final.} = distinct int
proc mainScreen: NSScreen {.importobjc: "NSScreen mainScreen", nodecl.}
proc scaleFactor(s: NSScreen): float32 = discard
proc screenScaleFactor*(): float =
    result = mainScreen().scaleFactor()

Traceback (most recent call last)
nim.nim(121)             nim
nim.nim(77)              handleCmdLine
main.nim(167)            mainCommand
main.nim(74)             commandCompileToC
modules.nim(240)         compileProject
modules.nim(180)         compileModule
passes.nim(217)          processModule
passes.nim(135)          processTopLevelStmt
cgen.nim(1331)           myProcess
ccgstmts.nim(1127)       genStmts
ccgexprs.nim(2221)       expr
cgen.nim(855)            genProc
cgen.nim(820)            genProcNoForward
cgen.nim(719)            genProcAux
ccgstmts.nim(1127)       genStmts
ccgexprs.nim(2171)       expr
ccgstmts.nim(1120)       genAsgn
ccgstmts.nim(85)         loadInto
ccgexprs.nim(2132)       expr
ccgexprs.nim(1669)       genConv
ccgexprs.nim(1612)       genSomeCast
cgen.nim(486)            initLocExpr
ccgexprs.nim(2112)       expr
ccgcalls.nim(537)        genCall
ccgcalls.nim(176)        genPrefixCall
ccgcalls.nim(159)        genArg
cgen.nim(491)            initLocExprSingleUse
ccgexprs.nim(2112)       expr
ccgcalls.nim(535)        genCall
ccgcalls.nim(524)        genNamedParamCall
ccgexprs.nim(281)        genAssignment
cgen.nim(66)             t
SIGSEGV: Illegal storage access. (Attempt to read from nil?)