Got to the bottom of it:
HAVE_QCA2 is set *after* the config.h is created in CMakeLists.txt, which
because CMaske is awful means the #define is never created.
(this appears to be an upstream bug, revision a4e0c5e9 or thereabouts)
diff --git a/CMakeLists.txt b/CMakeLists.txt
index cd5fe62..390dec8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -52,11 +52,11 @@ check_include_file("stropts.h" HAVE_STROPTS_H)
check_include_file("byteswap.h" HAVE_BYTESWAP_H)
check_include_file("sys/endian.h" HAVE_SYS_ENDIAN_H)
+set(HAVE_QCA2 ${Qca-qt5_FOUND})
+
configure_file(config-konversation.h.cmake ${CMAKE_CURRENT_BINARY_DIR}/config-
konversation.h )
include_directories(${CMAKE_CURRENT_BINARY_DIR})
-set(HAVE_QCA2 ${Qca-qt5_FOUND})
-
add_definitions(
-DQT_USE_QSTRINGBUILDER
-DQT_NO_CAST_TO_ASCII
