Sweep out some extra warnings

Swept:
`-Wpadded` in some places (where it caused extra size, instead of just
saying "hey, we padded struct at the end to align, just as standard says")
`-Wweak-vtables` everywhere (Clang)
`-Wexit-time-destructors` everywhere (Clang)
`-Wmissing-noreturn` everywhere (Clang)

The last three are enabled for Clang compilation going forward.

Also enabled `-Wunreachable-code` for Clang and GCC

projects/SelfTest/SurrogateCpps/catch_interfaces_capture.cpp

@@ -1,3 +0,0 @@
-// This file is only here to verify (to the extent possible) the self sufficiency of the header
-#include "internal/catch_suppress_warnings.h"
-#include "internal/catch_interfaces_capture.h"

projects/SelfTest/SurrogateCpps/catch_interfaces_config.cpp

@@ -1,2 +0,0 @@
-#include "internal/catch_suppress_warnings.h"
-#include "internal/catch_interfaces_config.h"

projects/SelfTest/SurrogateCpps/catch_interfaces_exception.cpp

@@ -1,2 +0,0 @@
-#include "internal/catch_suppress_warnings.h"
-#include "internal/catch_interfaces_exception.h"

projects/SelfTest/SurrogateCpps/catch_interfaces_registry_hub.cpp

@@ -1,3 +0,0 @@
-// This file is only here to verify (to the extent possible) the self sufficiency of the header
-#include "internal/catch_suppress_warnings.h"
-#include "internal/catch_interfaces_registry_hub.h"

projects/SelfTest/SurrogateCpps/catch_interfaces_runner.cpp

@@ -1 +0,0 @@
-#include "internal/catch_interfaces_runner.h"

projects/SelfTest/SurrogateCpps/catch_interfaces_testcase.cpp

@@ -1,2 +0,0 @@
-#include "internal/catch_suppress_warnings.h"
-#include "internal/catch_interfaces_testcase.h"

projects/SelfTest/SurrogateCpps/catch_streambuf.cpp

@@ -1,3 +0,0 @@
-// This file is only here to verify (to the extent possible) the self sufficiency of the header
-#include "internal/catch_suppress_warnings.h"
-#include "internal/catch_streambuf.h"