Suppress spurious warning about RCTCxxModule (#19880)

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On a relatively stock / default setup of RN on iOS you'll see the warning "Class RCTCxxModule was not exported. Did you forget to use RCT_EXPORT_MODULE()?" pop up on every launch. This change resolves that issue.

Fixes #14806 .

This supersedes PR #19794 .

Try a fresh project by following the RN iOS tutorial, and observe that there are no more warnings after making this change.

[IOS] [MINOR] [CxxBridge] - Fix "Class RCTCxxModule was not exported"
Closes facebook/react-native#19880

Differential Revision: D8653809

Pulled By: hramos

fbshipit-source-id: c48529c2d74ddd40a90bc0e06e405078e25b72e3

React/Base/RCTBridge.m

@@ -98,6 +98,9 @@ void RCTVerifyAllModulesExported(NSArray *extraModules)
 
   for (unsigned int i = 0; i < classCount; i++) {
     Class cls = classes[i];
+    if (strncmp(class_getName(cls), "RCTCxxModule", strlen("RCTCxxModule")) == 0) {
+      continue;
+    }
     Class superclass = cls;
     while (superclass) {
       if (class_conformsToProtocol(superclass, @protocol(RCTBridgeModule))) {