There are a couple errors in toolchain/helpers.mk in the check_glibc function. First, the strip $1 appears to remove everything, not just the trailing '/'. Second, the test command has a typo; it references SYSDROOT_DIR instead of SYSROOT_DIR.
The SYSDROOT problem has been fixed in 666eb02be3cd4115a1ef8b78a63d64d12b24469e. I'm not sure to understand the other problem, the check_glibc function seems to work fine here. If you think there is still a problem, do not hesitate to reopen this bug.