[asan] Fix nonsensical reports of partial right OOB.

In case of partial right OOB, ASan was reporting
  X is located 0 bytes to the right of [A, B)
where X was actually inside [A, B).

With this change, ASan will report B as the error address in such case.

llvm-svn: 174373
diff --git a/compiler-rt/lib/asan/lit_tests/strncpy-overflow.cc b/compiler-rt/lib/asan/lit_tests/strncpy-overflow.cc
index 2d79c7a..5133b5c 100644
--- a/compiler-rt/lib/asan/lit_tests/strncpy-overflow.cc
+++ b/compiler-rt/lib/asan/lit_tests/strncpy-overflow.cc
@@ -22,7 +22,7 @@
   strcpy(hello, "hello");
   char *short_buffer = (char*)malloc(9);
   strncpy(short_buffer, hello, 10);  // BOOM
-  // CHECK: {{WRITE of size 1 at 0x.* thread T0}}
+  // CHECK: {{WRITE of size 10 at 0x.* thread T0}}
   // CHECK-Linux: {{    #0 0x.* in .*strncpy}}
   // CHECK-Darwin: {{    #0 0x.* in _?wrap_strncpy}}
   // CHECK: {{    #1 0x.* in _?main .*strncpy-overflow.cc:}}[[@LINE-4]]