The Linux kernel source relies on a case sensitive filesystem. If you attempt to get the sources via git this will manifest as an error along the lines of:
fatal: Entry 'include/linux/netfilter/xt_CONNMARK.h
There are several header files like this the names of which differ only in case and just can’t be represented on a filesystem that doesn’t distinguish between cases. This is most commonly seen by people attempting to build embedded Linux from Windows.