[Axccel] Remove -Wno-missing-braces in build

[jhen]

Summary

I originally added the -Wno-missing-braces flag because I thought it was
erroneously flagging std::array initializations. Now I realize the extra
braces really are desired for these initializations, so I'm turning the
warning flag back on.

acxxel/CMakeLists.txt

 configure_file(config.h.in config.h)
 include_directories(${CMAKE_CURRENT_BINARY_DIR})
 
 # Insist on C++ 11 features.
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 # Add warning flags.
-set(CMAKE_CXX_FLAGS  "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wno-missing-braces")
+set(CMAKE_CXX_FLAGS  "${CMAKE_CXX_FLAGS} -Wall -Wextra")
 
 add_library(
     acxxel
     acxxel.cpp
     ${ACXXEL_CUDA_SOURCES}
     ${ACXXEL_OPENCL_SOURCES})
 target_link_libraries(
     acxxel

acxxel/examples/opencl_example.cpp

if (Status.isError()) {
     std::fprintf(stderr, "Error during saxpy: %s\n",
                  Status.getMessage().c_str());
     std::exit(EXIT_FAILURE);
   }
 }
 
 int main() {
   float A = 2.f;
-  std::array<float, 3> X = {0.f, 1.f, 2.f};
-  std::array<float, 3> Y = {3.f, 4.f, 5.f};
-  std::array<float, 3> Expected = {3.f, 6.f, 9.f};
+  std::array<float, 3> X{{0.f, 1.f, 2.f}};
+  std::array<float, 3> Y{{3.f, 4.f, 5.f}};
+  std::array<float, 3> Expected{{3.f, 6.f, 9.f}};
   saxpy(A, X, Y);
   for (int I = 0; I < 3; ++I)
     if (X[I] != Expected[I]) {
       std::fprintf(stderr, "Mismatch at position %d, %f != %f\n", I, X[I],
                    Expected[I]);
       std::exit(EXIT_FAILURE);
     }
 }

acxxel/tests/span_test.cpp

 TEST(Span, ArrayConstruction) {
   int Array[] = {0, 1, 2};
   acxxel::Span<int> Span(Array);
   EXPECT_EQ(Span.data(), Array);
   EXPECT_EQ(Span.size(), 3);
 }
 
 TEST(Span, StdArrayConstruction) {
-  std::array<int, 3> Array{0, 1, 2};
+  std::array<int, 3> Array{{0, 1, 2}};
   acxxel::Span<int> Span(Array);
   EXPECT_EQ(Span.data(), Array.data());
   EXPECT_EQ(static_cast<size_t>(Span.size()), Array.size());
 
-  std::array<const int, 3> ConstArray{0, 1, 2};
+  std::array<const int, 3> ConstArray{{0, 1, 2}};
   acxxel::Span<const int> ConstSpan(ConstArray);
   EXPECT_EQ(ConstSpan.data(), ConstArray.data());
   EXPECT_EQ(static_cast<size_t>(ConstSpan.size()), ConstArray.size());
 }
 
 TEST(Span, ContainerConstruction) {
   std::vector<int> Vector = {0, 1, 2};
   acxxel::Span<int> Span(Vector);