Tweak use of AC_USE_SYSTEM_EXTENSIONS

This makes sure that `AC_USE_SYSTEM_EXTENSIONS` (which
implies `AC_PROG_CC`) is called after the
`AC_ARG_WITH([cc],,)` invocation, so that the proper
CC setting is in scope. Otherwise this can break cross-compilation.

This also needs to pull in a submodule update for `unix`

This is a follow-up commit to
7af29da05d2e5a5e311a5f73f20d0f232035973b
which hopefully fixes #11168

1 files changed, 0 insertions, 0 deletions

diff --git a/libraries/unix b/libraries/unix
-Subproject 5740003e06f0c585460501514f3352f5e105c98
+Subproject 147630c7c76bd9b947524ef140d21b9e81967c6