Add -match-full-lines argument to FileCheck.

This is useful for some tests where more-exact matching is useful, such
as clang's Preprocessor tests.

llvm-svn: 260540
diff --git a/llvm/docs/CommandGuide/FileCheck.rst b/llvm/docs/CommandGuide/FileCheck.rst
index 03c8829..8d88237 100644
--- a/llvm/docs/CommandGuide/FileCheck.rst
+++ b/llvm/docs/CommandGuide/FileCheck.rst
@@ -42,6 +42,18 @@
 
   File to check (defaults to stdin).
 
+.. option:: --match-full-lines
+
+ By default, FileCheck allows matches of anywhere on a line. This
+ option will require all positive matches to cover an entire
+ line. Leading and trailing whitespace is ignored, unless
+ :option:`--strict-whitespace` is also specified. (Note: negative
+ matches from ``CHECK-NOT`` are not affected by this option!)
+
+ Passing this option is equivalent to inserting ``{{^ *}}`` or
+ ``{{^}}`` before, and ``{{ *$}}`` or ``{{$}}`` after every positive
+ check pattern.
+
 .. option:: --strict-whitespace
 
  By default, FileCheck canonicalizes input horizontal whitespace (spaces and