Code cleanup: fix no previous declaration warnings

Moved some internally used functions into an anonymous namespace.

Change-Id: Ie82df61b0608abac79ccc9f7b14e7f7e04ab733d

internal/ceres/polynomial.cc

diff --git a/internal/ceres/polynomial.cc b/internal/ceres/polynomial.cc
index c4b0243..75f43de 100644
--- a/internal/ceres/polynomial.cc
+++ b/internal/ceres/polynomial.cc
@@ -120,7 +120,6 @@
   }
   return polynomial_in.tail(polynomial_in.size() - i);
 }
-}  // namespace
 
 void FindLinearPolynomialRoots(const Vector& polynomial,
                                Vector* real,
@@ -178,6 +177,7 @@
     (*imaginary)(1) = -sqrt_D / (2.0 * a);
   }
 }
+}  // namespace
 
 bool FindPolynomialRoots(const Vector& polynomial_in,
                          Vector* real,