unittests/FEXLinuxTests: Adds 64-bit vsyscall test

We never actually had a unittest to ensure these keep working, so add
one now.

unittests/FEXLinuxTests/tests/syscalls/vsyscall.64.cpp

@@ -0,0 +1,26 @@
+#include <cstdint>
+#include <sys/time.h>
+
+using gettime_type = int (*)(struct timeval* tv, struct timezone* tz);
+gettime_type gettimeofday_vsyscall = (gettime_type)0xFFFF'FFFF'FF60'0000ULL;
+
+using time_type = int (*)(time_t* tloc);
+time_type time_vsyscall = (time_type)0xFFFF'FFFF'FF60'0400ULL;
+
+using getcpu_type = int (*)(uint32_t* cpu, uint32_t* node);
+getcpu_type getcpu_vsyscall = (getcpu_type)0xFFFF'FFFF'FF60'0800ULL;
+
+int main() {
+  // This test just ensures that these vsyscalls execute without crashing.
+  // FEX has broken vsyscalls periodically.
+  timeval tv {};
+  gettimeofday_vsyscall(&tv, nullptr);
+
+  time_t tloc {};
+  time_vsyscall(&tloc);
+
+  uint32_t cpu, node;
+  getcpu_vsyscall(&cpu, &node);
+
+  return 0;
+}