[scudo] Fix an edge case in the secondary allocator

Summary:
s/CHECK_LT/CHECK_LE/ in the secondary allocator, as under certain circumstances
Ptr + Size can be equal to MapEnd. This edge case was not found by the current
tests, so those were extended to be able to catch that.

Reviewers: kcc

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D25101

llvm-svn: 282913
diff --git a/compiler-rt/lib/scudo/scudo_allocator.cpp b/compiler-rt/lib/scudo/scudo_allocator.cpp
index 7dd400e..9b86cfd 100644
--- a/compiler-rt/lib/scudo/scudo_allocator.cpp
+++ b/compiler-rt/lib/scudo/scudo_allocator.cpp
@@ -81,9 +81,9 @@
   u8  Unused_0_     : 4;
   // 2nd 8 bytes
   u64 Offset        : 20; // Offset from the beginning of the backend
-                          // allocation to the beginning chunk itself, in
-                          // multiples of MinAlignment. See comment about its
-                          // maximum value and test in init().
+                          // allocation to the beginning of the chunk itself,
+                          // in multiples of MinAlignment. See comment about
+                          // its maximum value and test in init().
   u64 Unused_1_     : 28;
   u16 Salt          : 16;
 };