CLSA-2021-1634922609 Fixed CVEs in glibc: CVE-2021-38604, CVE-2021-35942, CVE-2021-33574

Adopt pthreadattrcopy functionality, test case is included - CVE-2021-33574: avoid use-after-free vulnerability - CVE-2021-35942: avoid out-of-bounds read via signed integer overflow in array index - CVE-2021-38604: considered. No NULL pointer dereference is possible...