[Bug libitm/88319] all-target and all-target-libitm build targets fail for libitm.

[schwab--- via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88319

--- Comment #5 from Andreas Schwab <sch...@linux-m68k.org> ---
Check the value of ac_cv_prog_CXX.