Add variation job with RC_DEBUG=1

This is also intended to test other default-disabled config
options in the future, e.g. PROFITABILITY_CHECKS=0.

azure-pipelines.yml

@@ -111,3 +111,9 @@ jobs:
       parameters:
         configurationName: LIBMYSQLCLIENT_DEBUG_NTS
         configurationParameters: '--enable-debug --disable-zts'
+    - template: azure/job.yml
+      parameters:
+        configurationName: VARIATION_DEBUG_ZTS
+        configurationParameters: >-
+            --enable-debug --enable-zts
+            CFLAGS="-DZEND_RC_DEBUG=1"