build-sys: update "linkcheck"

<kay> ssuominen: and drop --no-as-needed from the linkcheck?
<kay> ssuominen: i expect it all triggers without the gc-sections thing alone
<ssuominen> if the intention is to make it strict as possible,
  to catch undefined references caused by missing -lfoo in linker line, then
  LDFLAGS="-Wl,-fuse-ld=gold -Wl,--as-needed -Wl,--no-gc-sections"