• Fix build errors due new gcc 10 default for -fno-common.
• In fixing, if a parity is filtered out, don't attempt to recover its size,
  and proceed without it if missing.
• Avoid unnecessary parity read when fixing the parity itself.
  This improves the 'fix' speed when a parity file is completely missing.
• Removed a build warning about major/minor defined now in sys/sysmacros.h.