Clang-format: Avoid hardcoded LLVM include-order style

Reported by:	emaste

.clang-format

@@ -134,6 +134,12 @@ IncludeCategories:
   - Regex: '^\".*\.h\"'
     Priority: 10
     SortPriority: 100
+# LLVM's header include ordering style is almost the exact opposite of ours.
+# Unfortunately, they have hard-coded their preferences into clang-format.
+# Clobbering this regular expression to avoid matching prevents non-system
+# headers from being forcibly moved to the top of the include list.
+# http://llvm.org/docs/CodingStandards.html#include-style
+IncludeIsMainRegex: 'BLAH_DONT_MATCH_ANYTHING'
 SortIncludes: true
 KeepEmptyLinesAtTheStartOfBlocks: true
 TypenameMacros: