cmake: Fix building against libiconv

packages/mariadb/libmariadb-libmariadb-CMakeLists.txt.patch

@@ -0,0 +1,11 @@
+diff -u -r ../mariadb-10.3.14/libmariadb/libmariadb/CMakeLists.txt ./libmariadb/libmariadb/CMakeLists.txt
+--- ../mariadb-10.3.14/libmariadb/libmariadb/CMakeLists.txt	2019-04-01 14:03:57.000000000 +0000
++++ ./libmariadb/libmariadb/CMakeLists.txt	2019-05-22 23:50:06.105346983 +0000
+@@ -302,7 +302,6 @@
+   IF(ICONV_INCLUDE_DIR)
+      INCLUDE_DIRECTORIES(BEFORE ${ICONV_INCLUDE_DIR}) 
+   ENDIF()
+-  ADD_DEFINITIONS(-DLIBICONV_PLUG)
+ ENDIF()
+ 
+ IF(ZLIB_FOUND AND WITH_EXTERNAL_ZLIB)