improve wx GCC ABI check #142

Following some suggestions from @ArtiiP, first check if there are no
issues without an -fabi-version flag, and then instead of incrementing
from 0, decrement from 15 to find the highest working ABI version.

This is very slow if the needed ABI version is 2 for example, but not
much to do about that for the time being.

src/wx/CMakeLists.txt

@@ -110,14 +110,30 @@ ENDIF()
 IF(CMAKE_COMPILER_IS_GNUCXX)
     INCLUDE(CheckCXXSourceRuns)
 
-    UNSET(WX_ABI_MATCHES)
+    CHECK_CXX_SOURCE_RUNS("
-    SET(WX_ABI_VERSION 0)
+#include <cstdlib>
+#include <wx/wx.h>
+
+class MyApp : public wxAppConsole {
+public:
+    virtual bool OnInit();
+};
+
+bool MyApp::OnInit() {
+    exit(0);
+}
+
+wxIMPLEMENT_APP(MyApp);
+" WX_DEFAULT_ABI_VERSION_COMPATIBLE)
+
+    IF(NOT WX_DEFAULT_ABI_VERSION_COMPATIBLE)
+        # currently goes up to 11 with gcc7, but we give it some room
+        SET(WX_ABI_VERSION 15)
 
         SET(CURRENT_DEFS ${CMAKE_REQUIRED_DEFINITIONS})
         SET(CURRENT_LIBS ${CMAKE_REQUIRED_LIBRARIES})
 
-    # currently goes up to 11 with gcc7, but we give it some room
+        WHILE(NOT WX_ABI_VERSION EQUAL -1)
-    WHILE(NOT WX_ABI_VERSION GREATER 15)
             SET(CMAKE_REQUIRED_DEFINITIONS ${CURRENT_DEFS} "-fabi-version=${WX_ABI_VERSION}")
             SET(CMAKE_REQUIRED_LIBRARIES   ${CURRENT_LIBS} "-fabi-version=${WX_ABI_VERSION}")
 
@@ -137,23 +153,24 @@ bool MyApp::OnInit() {
 }
 
 wxIMPLEMENT_APP(MyApp);
-" ${WX_ABI_VAR})
+    " ${WX_ABI_VAR})
 
             IF(${${WX_ABI_VAR}})
                 BREAK()
             ENDIF()
 
-        MATH(EXPR WX_ABI_VERSION "${WX_ABI_VERSION} + 1")
+            MATH(EXPR WX_ABI_VERSION "${WX_ABI_VERSION} - 1")
         ENDWHILE()
 
         SET(CMAKE_REQUIRED_DEFINITIONS ${CURRENT_DEFS})
         SET(CMAKE_REQUIRED_LIBRARIES   ${CURRENT_LIBS})
 
-    IF(${${WX_ABI_VAR}} AND (NOT WX_ABI_VERSION EQUAL 0))
+        IF(${${WX_ABI_VAR}})
             # add C++ flags
             STRING(REGEX REPLACE "<FLAGS>" "<FLAGS> -fabi-version=${WX_ABI_VERSION} " CMAKE_CXX_COMPILE_OBJECT ${CMAKE_CXX_COMPILE_OBJECT})
             SET(CMAKE_CXX_LINK_EXECUTABLE "${CMAKE_CXX_LINK_EXECUTABLE} -fabi-version=${WX_ABI_VERSION}")
         ENDIF()
+    ENDIF()
 ENDIF()
 
 # end of wx compile checks