configure.ac: fix maybe-uninitialized for clang

Clang and gcc have different names for this, but the check fails without
-Werror since clang only warns about unknown args.

The previous check led to a lot of "unknown arg" spam while compiling
with clang.

Change-Id: Iad6c16beed26d5fe8952d7d5a79a93845c391b48
1 file changed