Fix missing declaration warnings in GCC

- Follow up to commit https://github.com/ceres-solver/ceres-solver/commit/54ba6c27b504f43b59b0d91da0165995c66d9a3d
  which enabled -Wmissing-declarations and fixed all previous
  infractions.

Change-Id: Ia10b49b4c9bc12c0f7bec2b8c0706f38be18f1dc

internal/ceres/invert_psd_matrix_benchmark.cc

diff --git a/internal/ceres/invert_psd_matrix_benchmark.cc b/internal/ceres/invert_psd_matrix_benchmark.cc
index 02a19f3..a10484f 100644
--- a/internal/ceres/invert_psd_matrix_benchmark.cc
+++ b/internal/ceres/invert_psd_matrix_benchmark.cc
@@ -62,7 +62,7 @@
 BENCHMARK_TEMPLATE(BenchmarkFixedSizedInvertPSDMatrix, 11);
 BENCHMARK_TEMPLATE(BenchmarkFixedSizedInvertPSDMatrix, 12);
 
-void BenchmarkDynamicallyInvertPSDMatrix(benchmark::State& state) {
+static void BenchmarkDynamicallyInvertPSDMatrix(benchmark::State& state) {
   using MatrixType =
       typename EigenTypes<Eigen::Dynamic, Eigen::Dynamic>::Matrix;
   const int size = state.range(0);

internal/ceres/schur_eliminator_benchmark.cc

diff --git a/internal/ceres/schur_eliminator_benchmark.cc b/internal/ceres/schur_eliminator_benchmark.cc
index 6307025..73bdfd9 100644
--- a/internal/ceres/schur_eliminator_benchmark.cc
+++ b/internal/ceres/schur_eliminator_benchmark.cc
@@ -127,7 +127,7 @@
   Vector y_;
 };
 
-void BM_SchurEliminatorEliminate(benchmark::State& state) {
+static void BM_SchurEliminatorEliminate(benchmark::State& state) {
   const int num_e_blocks = state.range(0);
   BenchmarkData data(num_e_blocks);
 
@@ -150,7 +150,7 @@
   }
 }
 
-void BM_SchurEliminatorBackSubstitute(benchmark::State& state) {
+static void BM_SchurEliminatorBackSubstitute(benchmark::State& state) {
   const int num_e_blocks = state.range(0);
   BenchmarkData data(num_e_blocks);
 
@@ -178,7 +178,7 @@
   }
 }
 
-void BM_SchurEliminatorForOneFBlockEliminate(benchmark::State& state) {
+static void BM_SchurEliminatorForOneFBlockEliminate(benchmark::State& state) {
   const int num_e_blocks = state.range(0);
   BenchmarkData data(num_e_blocks);
   SchurEliminatorForOneFBlock<2, 3, 6> eliminator;
@@ -192,7 +192,7 @@
   }
 }
 
-void BM_SchurEliminatorForOneFBlockBackSubstitute(benchmark::State& state) {
+static void BM_SchurEliminatorForOneFBlockBackSubstitute(benchmark::State& state) {
   const int num_e_blocks = state.range(0);
   BenchmarkData data(num_e_blocks);
   SchurEliminatorForOneFBlock<2, 3, 6> eliminator;

internal/ceres/small_blas_gemv_benchmark.cc

diff --git a/internal/ceres/small_blas_gemv_benchmark.cc b/internal/ceres/small_blas_gemv_benchmark.cc
index 4b587bf..824f0eb 100644
--- a/internal/ceres/small_blas_gemv_benchmark.cc
+++ b/internal/ceres/small_blas_gemv_benchmark.cc
@@ -78,7 +78,7 @@
   }
 }
 
-void BM_MatrixVectorMultiply(benchmark::State& state) {
+static void BM_MatrixVectorMultiply(benchmark::State& state) {
   const int rows = state.range(0);
   const int cols = state.range(1);
   MatrixVectorMultiplyData data(rows, cols);
@@ -94,7 +94,7 @@
 
 BENCHMARK(BM_MatrixVectorMultiply)->Apply(MatrixSizeArguments);
 
-void BM_MatrixTransposeVectorMultiply(benchmark::State& state) {
+static void BM_MatrixTransposeVectorMultiply(benchmark::State& state) {
   const int rows = state.range(0);
   const int cols = state.range(1);
   MatrixVectorMultiplyData data(cols, rows);

internal/ceres/small_blas_test.cc

diff --git a/internal/ceres/small_blas_test.cc b/internal/ceres/small_blas_test.cc
index 2dde17e..6d02995 100644
--- a/internal/ceres/small_blas_test.cc
+++ b/internal/ceres/small_blas_test.cc
@@ -73,7 +73,7 @@
 #undef MATRIX_FUN_TY
 
 // Initializes matrix entires.
-void initMatrix(Matrix &mat) {
+static void initMatrix(Matrix &mat) {
   for (int i = 0; i < mat.rows(); ++i) {
     for (int j = 0; j < mat.cols(); ++j) {
       mat(i, j) = i + j + 1;