[sanitizer] Add basic qsort test

compiler-rt/test/sanitizer_common/TestCases/Posix/qsort.cpp

@@ -0,0 +1,24 @@
+// RUN: %clangxx -O2 %s -o %t
+
+#include <algorithm>
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <vector>
+
+static int compare_ints(const void *a, const void *b) {
+  return *(const int *)b - *(const int *)a;
+}
+
+int main() {
+  std::vector<int> nums(100000);
+  for (auto &n : nums)
+    n = rand();
+
+  std::vector<int> to_qsort = nums;
+  qsort(to_qsort.data(), to_qsort.size(), sizeof(to_qsort[0]), &compare_ints);
+
+  std::sort(nums.begin(), nums.end());
+
+  assert(nums == to_qsort);
+}