Fix a bogus MSVC linker error.

MSVC cannot handle `extern` declarations inside a member function,
when that member function is itself inside a namespace: it "forgets"
the namespace part when generating the symbol, which leads in this case
to an "unresolved symbol" error at link time.

Reduced example: https://godbolt.org/z/YSQ--9

Author: Quuxplusone

hyper.h

@@ -4218,6 +4218,9 @@ void virtualRebaseSimple(heptagon*& base, transmatrix& at);
 
 extern bool game_active, playerfound;
 
+extern bool twopoint_do_flips;
+extern int twopoint_sphere_flips;
+
 string bygen(reaction_t h);
 
 #if CAP_URL

polygons.cpp

@@ -867,8 +867,6 @@ void dqi_poly::draw() {
   if(sphere && pmodel == mdTwoPoint && !in_twopoint) {
     #define MAX_PHASE 4
     vector<glvertex> phases[MAX_PHASE];
-    extern int twopoint_sphere_flips;
-    extern bool twopoint_do_flips;
     int pha;
     if(twopoint_do_flips) {
       for(int i=0; i<cnt; i++) {