test: synchronise lit substitutions

llvm-strings was added to the test dependencies without updating the lit
substitutions.  Synchronise the list.

llvm-svn: 286773

llvm/test/lit.cfg

@@ -307,6 +307,7 @@ for pattern in [r"\bbugpoint\b(?!-)",
                 r"\bllvm-rtdyld\b",
                 r"\bllvm-size\b",
                 r"\bllvm-split\b",
+                r"\bllvm-strings\b",
                 r"\bllvm-tblgen\b",
                 r"\bllvm-c-test\b",
                 r"\bllvm-cxxfilt\b",