elifdef is C23

And the new clang complains (-Wc++23-extensions)

benchmarks/timing.h

diff --git a/benchmarks/timing.h b/benchmarks/timing.h
index 066323e..2d4bf04 100644
--- a/benchmarks/timing.h
+++ b/benchmarks/timing.h
@@ -12,7 +12,7 @@
 		// On Sail, report the number of instructions, the cycle count is
 		// meaningless.
 		__asm__ volatile("csrr %0, minstret" : "=r"(cycles));
-#elifdef IBEX
+#elif defined(IBEX)
 		// CHERIoT-Ibex does not yet implement rdcycle, so read the CSR
 		// directly.
 		__asm__ volatile("csrr %0, mcycle" : "=r"(cycles));