clang compile error on gcc bound member function

[rockeet]

gcc feature: https://gcc.gnu.org/onlinedocs/gcc/Bound-member-functions.html

clang does not support this feature.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: rockeet (rockeet)

gcc feature: https://gcc.gnu.org/onlinedocs/gcc/Bound-member-functions.html

clang does not support this feature.

[shafik]

CC @erichkeane @AaronBallman