Running multiple fuzz tests segfaults

### Zig Version 0.16.0-dev.1456+16fc083f2 ### Steps to Reproduce and Observed Behavior Zig downloaded from the downloads page: [zig-x86_64-linux-0.16.0-dev.1456+16fc083f2.tar.xz](https://ziglang.org/builds/zig-x86_64-linux-0.16.0-dev.1456+16fc083f2.tar.xz) Running multiple fuzz tests at the same time cases a segfault error: ``` zig build fuzz --fuzz -Doptimize=ReleaseSafe -j64 info(web_server): web interface listening at http://[::1]:43323/ info(web_server): hint: pass '--webui=[::1]:43323' to use the same port next time Build Summary: 7/7 steps succeeded; 2/2 tests passed Segmentation fault at address 0x7f6a022520e8 /home/ozgur/zig/out/lib/std/heap/debug_allocator.zig:907:23: 0x12607d4 in free (std.zig) if (bucket.canary != config.canary) @panic("Invalid free"); ^ /home/ozgur/zig/out/lib/std/mem/Allocator.zig:160:25: 0x1122789 in rawFree (std.zig) return a.vtable.free(a.ptr, memory, alignment, ret_addr); ^ /home/ozgur/zig/out/lib/std/Build/Step/Run.zig:1145:22: 0x131728c in rerunInFuzzMode (std.zig) fuzz.gpa.free(cmd); ^ /home/ozgur/zig/out/lib/std/Build/Fuzz.zig:206:24: 0x1317ff1 in fuzzWorkerRun (std.zig) run.rerunInFuzzMode(fuzz, unit_test_index, prog_node) catch |err| switch (err) { ^ /home/ozgur/zig/out/lib/std/Thread/Pool.zig:118:39: 0x1318412 in runFn (std.zig) @call(.auto, func, closure.arguments); ^ /home/ozgur/zig/out/lib/std/Thread/Pool.zig:293:27: 0x1365c40 in worker (std.zig) runnable.runFn(runnable, id); ^ /home/ozgur/zig/out/lib/std/Thread.zig:559:13: 0x12d3bd0 in callFn__anon_82208 (std.zig) @call(.auto, f, args); ^ /home/ozgur/zig/out/lib/std/Thread.zig:1535:30: 0x1299ec0 in entryFn (std.zig) return callFn(f, self.fn_args); ^ /home/ozgur/zig/out/lib/std/os/linux/x86_64.zig:105:5: 0x11782b5 in clone (std.zig) asm volatile ( ^ error: the following build command crashed: .zig-cache/o/f7cec3636184dd88ed02791b925daf2f/build /home/ozgur/zig/out/zig /home/ozgur/zig/out/lib /home/ozgur/repos/olive .zig-cache /home/ozgur/.cache/zig --seed 0x4858de98 -Z77191c04cb9254a0 fuzz --fuzz -Doptimize=ReleaseSafe -j64 ``` Seems like the new fuzz test running logic is broken. Reverting to 0.16.0-dev.312+164c598cd fixes the issue for me. Not sure if this issue happens when there is a single fuzz test entrypoint. ### Expected Behavior Fuzzing shouldn't cause crash