This patch fixes "Argument list too long" build failure when passing a
list of store paths to system.extraDependencies that exceeds Linux'
MAX_ARG_STRLEN limit of 128 KiB. With the shortest possible derivation
names (one byte), the 128 KiB limit is equivalent to about 2850
derivations. With longer derivations names, the limit is hit earlier.
Fix this restriction.
ef85c3fe51