libfuzzer test: use proper cache dir logic

Author: tjog

test/standalone/libfuzzer/build.zig

@@ -22,5 +22,6 @@ pub fn build(b: *std.Build) void {
     b.default_step = run_step;
 
     const run_artifact = b.addRunArtifact(exe);
+    run_artifact.addArg(b.cache_root.path orelse "");
     run_step.dependOn(&run_artifact.step);
 }

test/standalone/libfuzzer/main.zig

@@ -15,7 +15,14 @@ extern fn fuzzer_init_corpus_elem(input_ptr: [*]const u8, input_len: usize) void
 extern fn fuzzer_coverage_id() u64;
 
 pub fn main() !void {
-    fuzzer_init(FuzzerSlice.fromSlice(""));
+    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
+    defer _ = gpa.deinit();
+    const args = try std.process.argsAlloc(gpa.allocator());
+    defer std.process.argsFree(gpa.allocator(), args);
+
+    const cache_dir = args[1];
+
+    fuzzer_init(FuzzerSlice.fromSlice(cache_dir));
     fuzzer_init_corpus_elem("hello".ptr, "hello".len);
     fuzzer_set_name("test".ptr, "test".len);
     _ = fuzzer_coverage_id();