[scudo] Skip AllocAfterFork test on machines with low max_map_count
Reducing the number of iterations in that test with D111342 helped,
but the failure still occured flakily when the test is ran as part
of a large test suite.
Reducing further the number of iterations might not be good enough,
so we will skip the test if the `max_map_count` variable can be
read, and if lower than a given threshold.
Differential Revision: https://reviews.llvm.org/D111465
1 file changed