[fuzzer] Fix TableLookupTest on FreeBSD

[andrew]

Summary

As with Linux placce the Counters array in the __libfuzzer_extra_counters
section. This fixes the test on FreeBSD.

compiler-rt/test/fuzzer/TableLookupTest.cpp

 // as extra coverage signal. The array must be:
 //  * uint8_t
 //  * in the section named __libfuzzer_extra_counters.
 // The target code may declare more than one such array.
 //
 // Use either `Counters[Idx] = 1` or `Counters[Idx]++;`
 // depending on whether multiple occurrences of the event 'Idx'
 // is important to distinguish from one occurrence.
-#ifdef __linux__
+#if defined(__linux__) || defined(__FreeBSD__)
 __attribute__((section("__libfuzzer_extra_counters")))
 #endif
 #ifdef _WIN32
 #  pragma section(".data$__libfuzzer_extra_counters")
 __declspec(allocate(".data$__libfuzzer_extra_counters"))
 #endif
     static uint8_t Counters[N];