Replace a ton of trivial #ifdefs with runtime checks

This one is big, but unless I missed something, should be all be
trivial.

scripted-diff with the following, then manually tweaked whatever needed:
```

if [ $# -ne 3 ]; then
    echo "Usage: $0 '<pattern>' '<replacement>' '<filename>'"
    exit 1
fi

pattern="$1"
replacement="$2"
filename="$3"

if [ ! -f "$filename" ]; then
    echo "Error: File $filename does not exist."
    exit 1
fi

sed -i '/'"$pattern"'/ {
    :loop
    $ !{
        N
        /'"$pattern"'.*\n.*#endif/ {
            s/'"$pattern"'/'"$replacement"'/
            s/#else/} else {/
            s/#endif/}/
            P
            D
        }
        /'"$pattern"'/ b loop
    }
}' "$filename"

echo "Replacement complete in $filename"
```

h/t to Grok2 for the sed command

sgp/sgp.cpp

@@ -58,6 +58,7 @@
 #endif
 #include <Music Control.h>
 
+#include <language.hpp>
 
 static void MAGIC(std::string const& aarrrrgggh = "")
 {}
@@ -858,13 +859,13 @@ int PASCAL HandledWinMain(HINSTANCE hInstance,	HINSTANCE hPrevInstance, LPSTR pC
 	}
 #endif
 
-#	ifdef ENGLISH
+	if( g_lang == i18n::Lang::en ) {
 	try
 	{
 		SetIntroType( INTRO_SPLASH );
 	}
 	HANDLE_FATAL_ERROR;
-#	endif
+	}
 
 	gfApplicationActive = TRUE;
 	gfProgramIsRunning = TRUE;