[lldb] Deflake TestTsanBasic.py

The test flaked on bots:
http://green.lab.llvm.org/green/job/lldb-cmake/38666/
The test expects that tsan will detect a single race
with concurrent memory accesses. TSan doesn't do this reliably.
Run 100 iterations of the racing threads, which should
make the race much more likely to be detected.

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D114444

lldb/test/API/functionalities/tsan/basic/main.c

@@ -16,14 +16,17 @@ void *f2(void *p) {
 
 int main (int argc, char const *argv[])
 {
-    pointer = (char *)malloc(10); // malloc line
+    for (int i = 0; i < 100; i++) {
+        pointer = (char *)malloc(10); // malloc line
 
-    pthread_t t1, t2;
-    pthread_create(&t1, NULL, f1, NULL);
-    pthread_create(&t2, NULL, f2, NULL);
+        pthread_t t1, t2;
+        pthread_create(&t1, NULL, f1, NULL);
+        pthread_create(&t2, NULL, f2, NULL);
 
-    pthread_join(t1, NULL);
-    pthread_join(t2, NULL);
+        pthread_join(t1, NULL);
+        pthread_join(t2, NULL);
 
+        free(pointer);
+    }
     return 0;
 }