Add LibreOffice Clang plugin to ExternalClangExamples.rst

Reviewers: rsmith, rizsotto.mailinglist

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D31133

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@298490 91177308-0d34-0410-b5e6-96231b3b80d8

Author: stbergmann

docs/ExternalClangExamples.rst

@@ -90,3 +90,11 @@ List of projects and tools
    You get more than 50 Qt related compiler warnings, ranging from unneeded
    memory allocations to misusage of API, including fix-its for automatic
    refactoring."
+
+`<https://gerrit.libreoffice.org/gitweb?p=core.git;a=blob_plain;f=compilerplugins/README;hb=HEAD>`_
+   "LibreOffice uses a Clang plugin infrastructure to check during the build
+   various things, some more, some less specific to the LibreOffice source code.
+   There are currently around 50 such checkers, from flagging C-style casts and
+   uses of reserved identifiers to ensuring that code adheres to lifecycle
+   protocols for certain LibreOffice-specific classes.  They may serve as
+   examples for writing RecursiveASTVisitor-based plugins."