libstdc++: Tweak timeout for testsuite/std/ranges/iota/max_size_type.cc

libstdc++: Tweak timeout for testsuite/std/ranges/iota/max_size_type.cc

A simulator can easily spend more than 10 minutes running
this test-case, and the default timeout is at 5 minutes.
Better allow even slower machines; use 4 as the factor.

Regarding relative runtime numbers (very local; mmixware simulator for
mmix-knuth-mmixware): test01 and test05 finish momentarily; test02 at
about 2 minutes, and test03 about 2m30, but test04 itself runs for
more than 6 minues and so times out.

Not sure if it's better to split up this test, as the excessive
runtime may be unintended, but this seemed simplest.

libstdc++-v3:
	* testsuite/std/ranges/iota/max_size_type.cc: Set
	dg-timeout-factor to 4.