Add -Wdeprecated to test suite and fix associated warnings (#1191)

This commit turns on `-Wdeprecated` in the test suite and fixes several
associated deprecation warnings that show up as a result:

- in C++17 `static constexpr` members are implicitly inline; our
  redeclaration (needed for C++11/14) is deprecated in C++17.

- various test suite classes have destructors and rely on implicit copy
  constructors, but implicit copy constructor definitions when a
  user-declared destructor is present was deprecated in C++11.

- Eigen also has various implicit copy constructors, so just disable
  `-Wdeprecated` in `eigen.h`.

tests/test_constants_and_functions.cpp

@@ -49,7 +49,14 @@ namespace test_exc_sp {
 int f1(int x) noexcept { return x+1; }
 int f2(int x) noexcept(true) { return x+2; }
 int f3(int x) noexcept(false) { return x+3; }
+#if defined(__GNUG__)
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wdeprecated"
+#endif
 int f4(int x) throw() { return x+4; } // Deprecated equivalent to noexcept(true)
+#if defined(__GNUG__)
+#  pragma GCC diagnostic pop
+#endif
 struct C {
     int m1(int x) noexcept { return x-1; }
     int m2(int x) const noexcept { return x-2; }
@@ -57,8 +64,15 @@ struct C {
     int m4(int x) const noexcept(true) { return x-4; }
     int m5(int x) noexcept(false) { return x-5; }
     int m6(int x) const noexcept(false) { return x-6; }
+#if defined(__GNUG__)
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wdeprecated"
+#endif
     int m7(int x) throw() { return x-7; }
     int m8(int x) const throw() { return x-8; }
+#if defined(__GNUG__)
+#  pragma GCC diagnostic pop
+#endif
 };
 }