[build] Disable array bounds checking for GCC

[build] Disable array bounds checking for GCC

The array bounds checker on GCC 12 and newer reports a very large
number of false positives that result in build failures.  In
particular, accesses through pointers to zero-length arrays (such as
those used by the linker table mechanism in include/ipxe/tables.h) are
reported as errors, contrary to the GCC documentation.

Work around this GCC issue by unconditionally disabling the warning.

Signed-off-by: Michael Brown <mcb30@ipxe.org>