Merge branch 'build_cmake' of https://github.com/TcT2k/wxWidgets

Add CMake-based build system.

Merge the original branch without any changes except for resolving the
conflict due to moving the contents of .travis.yml to a separate file by
propagating the changes done in this file since then to the new script
and rerunning ./build/update-setup-h and ./build/cmake/update_files.py
to update the file lists changed in the meanwhile.

Closes https://github.com/wxWidgets/wxWidgets/pull/330

build/cmake/lib/core/CMakeLists.txt

@@ -0,0 +1,52 @@
+#############################################################################
+# Name:        build/cmake/lib/core/CMakeLists.txt
+# Purpose:     CMake file for core library
+# Author:      Tobias Taschner
+# Created:     2016-10-01
+# Copyright:   (c) 2016 wxWidgets development team
+# Licence:     wxWindows licence
+#############################################################################
+
+include(../../source_groups.cmake)
+
+wx_option(wxUSE_IMAGE "use wxImage class" ON)
+
+wx_append_sources(CORE_SRC GUI_CMN)
+wx_append_sources(CORE_SRC BASE_AND_GUI_CMN)
+if(WIN32)
+    wx_append_sources(CORE_SRC BASE_AND_GUI_WIN32)
+elseif(UNIX)
+    wx_append_sources(CORE_SRC UNIX)
+endif()
+
+if(WXMSW)
+    wx_append_sources(CORE_SRC MSW_LOWLEVEL)
+    wx_append_sources(CORE_SRC MSW_DESKTOP_LOWLEVEL)
+    wx_append_sources(CORE_SRC MSW)
+    wx_append_sources(CORE_SRC MSW_DESKTOP)
+elseif(WXGTK)
+    wx_append_sources(CORE_SRC GTK2_LOWLEVEL)
+    wx_append_sources(CORE_SRC GTK2)
+
+    wx_append_sources(CORE_SRC XWIN_LOWLEVEL)
+elseif(WXOSX_COCOA)
+    wx_append_sources(CORE_SRC BASE_AND_GUI_OSX_COCOA)
+    wx_append_sources(CORE_SRC OSX_LOWLEVEL)
+    wx_append_sources(CORE_SRC OSX_SHARED)
+    wx_append_sources(CORE_SRC OSX_COCOA)
+endif()
+
+wx_add_library(core ${CORE_SRC})
+foreach(lib JPEG PNG TIFF)
+    if(${lib}_LIBRARIES)
+        if(lib STREQUAL JPEG)
+            wx_lib_include_directories(core PRIVATE ${${lib}_INCLUDE_DIR})
+        else()
+            wx_lib_include_directories(core PRIVATE ${${lib}_INCLUDE_DIRS})
+        endif()
+
+        wx_lib_link_libraries(core PRIVATE ${${lib}_LIBRARIES})
+    endif()
+endforeach()
+
+wx_finalize_lib(core)