more multi-thread fixes

don't use static on acquire()
don't yield at all
run fillBuf() on thread
fix option tooltip as it introduces some overhead

src/engine/platform/segapcm.cpp

@@ -27,7 +27,7 @@
 #define chWrite(c,a,v) rWrite(((c)<<3)+(a),v)
 
 void DivPlatformSegaPCM::acquire(short** buf, size_t len) {
-  static int os[2];
+  thread_local int os[2];
 
   for (size_t h=0; h<len; h++) {
     while (!writes.empty()) {