rts/M32Alloc: Abort if m32 linker mmap fails
rts/M32Alloc: Abort if m32 linker mmap fails

Previously we should just blinding dereference a NULL pointer.

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc