[PATCH] restore -fno-unit-at-a-time on GCC >= 4

[PATCH] restore -fno-unit-at-a-time on GCC >= 4

-fno-unit-at-a-time was removed for gcc >= 4 in order to
support gcc 4.2. Unfortunately, this caused nasty problems
in many modules which had some of their read-only parameters
optimized away.

So we have to restore -fno-unit-at-a-time for the moment.
This will break gcc 4.2 again, and another solution will be
needed in order to support it. Note that -fno-unit-at-a-time
may not be supported in future versions of gcc.

Signed-off-by: Willy Tarreau <w@1wt.eu>