Don't include <cassert>. (#2148) (#2152)

* Don't include <cassert>. (#2148)

This commit replaces use of the assert() macro in format-inl.h with
FMT_ASSERT(). This allows us to drop the cassert include.

* FMT_GCC_VERSION is not defined when we include test-assert.h, use __GCC__ instead.

* Don't explicitly suppress GCC's -Wterminate in tests' FMT_ASSERT.

Throwing from a separate function is enough to silence the warning, no need to
explicitly suppress it.

* Remove messages from assertions added in 2f699d2.

* Correct formatting around throw_assertion_failure().

test/test-assert.h

@@ -22,8 +22,14 @@ class assertion_failure : public std::logic_error {
 
 void assertion_failure::avoid_weak_vtable() {}
 
+// We use a separate function (rather than throw directly from FMT_ASSERT) to
+// avoid GCC's -Wterminate warning when FMT_ASSERT is used in a destructor.
+inline void throw_assertion_failure(const char* message) {
+  throw assertion_failure(message);
+}
+
 #define FMT_ASSERT(condition, message) \
-  if (!(condition)) throw assertion_failure(message);
+  if (!(condition)) throw_assertion_failure(message);
 
 // Expects an assertion failure.
 #define EXPECT_ASSERT(stmt, message) \