[ReleaseNotes] MemorySanitizer support of ASLR on FreeBSD

Reviewers: sylvestre.ledru, kcc

Reviewed By: sylvestre.ledru

Differential Revision: https://reviews.llvm.org/D66792

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@370035 91177308-0d34-0410-b5e6-96231b3b80d8

docs/MemorySanitizer.rst

@@ -204,6 +204,9 @@ Limitations
   non-position-independent executables, and could fail on some Linux
   kernel versions with disabled ASLR. Refer to documentation for older versions
   for more details.
+* MemorySanitizer might be incompatible with position-independent executables
+  from FreeBSD 13 but there is a check done at runtime and throws a warning
+  in this case.
 
 Current Status
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