[IRGen] Fix placeholder logic for emission of conditionally inverted protocols

rdar://153681688

Instead fo counting the actual conformances, the logic took the size of the bit field, i.e. used the highest set bit, so when a type had a conditional conformance only on ~Escapable, but not on ~Copyable, it would still add 2 placeholders, but only fill one.

lib/IRGen/GenMeta.cpp

@@ -1394,12 +1394,13 @@ namespace {
 
       // Create placeholders for the counts of the conditional requirements
       // for each conditional conformance to a supressible protocol.
-      unsigned numProtocols = countBitsUsed(protocols.rawBits());
+      unsigned numProtocols = 0;
       using PlaceholderPosition =
           ConstantAggregateBuilderBase::PlaceholderPosition;
       SmallVector<PlaceholderPosition, 2> countPlaceholders;
-      for (unsigned i : range(0, numProtocols)) {
+      for (auto kind : protocols) {
-        (void)i;
+        (void)kind;
+        numProtocols++;
         countPlaceholders.push_back(
             B.addPlaceholderWithSize(IGM.Int16Ty));
       }

validation-test/IRGen/rdar153681688.swift

@@ -0,0 +1,8 @@
+// RUN: %target-swift-frontend %s -target %target-swift-5.9-abi-triple -emit-ir
+
+public enum Enum<T : ~Escapable> : ~Escapable {
+  case none
+  case some(T)
+}
+
+extension Enum: Escapable where T: Escapable {}