[lsan][test] Add malloc(0) and realloc(p, 0) tests

compiler-rt/test/lsan/TestCases/malloc_zero.c

@@ -0,0 +1,15 @@
+// RUN: %clang_lsan %s -o %t
+// RUN: %env_lsan_opts=use_stacks=0 not %run %t 2>&1 | FileCheck %s
+
+#include <stdio.h>
+#include <stdlib.h>
+
+// CHECK: {{Leak|Address}}Sanitizer: detected memory leaks
+// CHECK: {{Leak|Address}}Sanitizer: 1 byte(s) leaked in 1 allocation(s).
+
+int main() {
+  // The behavior of malloc(0) is implementation-defined.
+  char *p = malloc(0);
+  fprintf(stderr, "zero: %p\n", p);
+  p = 0;
+}

compiler-rt/test/lsan/TestCases/realloc_zero.c

@@ -0,0 +1,13 @@
+// RUN: %clang_lsan %s -o %t
+// RUN: %run %t
+
+#include <assert.h>
+#include <stdlib.h>
+
+int main() {
+  char *p = malloc(1);
+  // The behavior of realloc(p, 0) is implementation-defined.
+  // We free the allocation.
+  assert(realloc(p, 0) == NULL);
+  p = 0;
+}