Extend C++17/C++14 feature checks to require unique_ptr

When testing compiler modes higher than C++11 for constructs we need,
include a check for using `unique_ptr` in that mode.  The PGI 18.4
compiler in some environments supports `unique_ptr` in C++11 mode
but is broken for C++14 and C++17.  Check that `unique_ptr` works
in these modes before using one.

Source/Checks/cm_cxx14_check.cmake

@@ -1,5 +1,5 @@
 set(CMake_CXX14_BROKEN 0)
-if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang|PGI")
   if(NOT CMAKE_CXX14_STANDARD_COMPILE_OPTION)
     set(CMake_CXX14_WORKS 0)
   endif()

Source/Checks/cm_cxx14_check.cpp

@@ -1,5 +1,8 @@
 #include <cstdio>
+#include <memory>
+
 int main()
 {
-  return 0;
+  std::unique_ptr<int> u(new int(0));
+  return *u;
 }

Source/Checks/cm_cxx17_check.cmake

@@ -1,5 +1,5 @@
 set(CMake_CXX17_BROKEN 0)
-if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang|PGI")
   if(NOT CMAKE_CXX17_STANDARD_COMPILE_OPTION)
     set(CMake_CXX17_WORKS 0)
   endif()

Source/Checks/cm_cxx17_check.cpp

@@ -1,7 +1,9 @@
 #include <cstdio>
+#include <memory>
 #include <unordered_map>
 
 int main()
 {
-  return 0;
+  std::unique_ptr<int> u(new int(0));
+  return *u;
 }