[XrdHttp] Fix XrdHttpProtocol layout mismatch when Kerberos is enabled

Export HAVE_HTTP_KRB5 to all XrdHttpUtils consumers so the XrdHttp
plugin allocates the same object size as the library constructor.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: apeters1971

src/XrdHttp/CMakeLists.txt

@@ -45,7 +45,9 @@ target_link_libraries(XrdHttpUtils
 )
 
 if(BUILD_KRB5)
-  target_compile_definitions(XrdHttpUtils PRIVATE HAVE_HTTP_KRB5)
+  # PUBLIC so all consumers of XrdHttpProtocol (e.g. the XrdHttp plugin)
+  # see the same class layout as XrdHttpUtils.
+  target_compile_definitions(XrdHttpUtils PUBLIC HAVE_HTTP_KRB5)
   target_include_directories(XrdHttpUtils PRIVATE ${KERBEROS5_INCLUDE_DIR})
   target_link_libraries(XrdHttpUtils PRIVATE ${KERBEROS5_LIBRARIES})
 endif()