Fix build on Mingw (KhronosGroup#574)

and add Mingw build to Github Actions.

CMakeLists.txt

@@ -326,14 +326,24 @@ macro(commom_lib_settings lib write)
         PUBLIC # only for basisu_c_binding.
             BASISU_NO_ITERATOR_DEBUG_LEVEL
         )
-        target_sources(
-            ${lib}
-        PRIVATE
-            # The msvs generator automatically sets the needed VCLinker
-            # option when a .def file is seen in sources.
-            lib/internalexport.def
-            $<${write}:lib/internalexport_write.def>
-        )
+        # The generator automatically sets the needed VCLinker
+        # option when a .def file is seen in sources.
+        # The def files that we add have a different syntax depending on the ABI
+        if(${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
+            target_sources(
+                ${lib}
+            PRIVATE
+                lib/internalexport_mingw.def
+                $<${write}:lib/internalexport_write_mingw.def>
+            )
+        else()
+            target_sources(
+                ${lib}
+            PRIVATE
+                lib/internalexport.def
+                $<${write}:lib/internalexport_write.def>
+            )
+        endif()
     elseif(EMSCRIPTEN)
         target_compile_definitions(${lib} PRIVATE
             # To reduce size, don't support transcoding to formats not

lib/filestream.c

@@ -52,6 +52,10 @@
   typedef unsigned short mode_t;
 #endif
 
+#if defined(__MINGW32__)
+    #define S_IFSOCK 0xC000
+#endif
+
 #define KTX_FILE_STREAM_MAX (1 << (sizeof(ktx_off_t) - 1) - 1)
 
 /**

lib/internalexport_mingw.def

@@ -0,0 +1,45 @@
+; Copyright 2019-2020 Mark Callow
+; SPDX-License-Identifier: Apache-2.0
+
+; Export internal functions used by internal test programs and the
+; validator. Using this file avoids having to decorate those internal
+; functions or updating such decorations as the tests evolve. Updating
+; this feels less obnoxious.
+
+LIBRARY libktx
+EXPORTS
+    _ZN6basist34basis_get_bytes_per_block_or_pixelENS_25transcoder_texture_formatE
+    _ZN6basist39basis_transcoder_format_is_uncompressedENS_25transcoder_texture_formatE
+    _ZN6basist38basis_get_uncompressed_bytes_per_pixelENS_25transcoder_texture_formatE
+    _ZNK6basist17basisu_transcoder15validate_headerEPKvj
+    _ZNK6basist17basisu_transcoder16get_total_imagesEPKvj
+    _ZNK6basist17basisu_transcoder20get_image_level_descEPKvjjjRjS3_S3_
+    _ZNK6basist17basisu_transcoder14get_image_infoEPKvjRNS_17basisu_image_infoEj
+    _ZNK6basist17basisu_transcoder20get_image_level_infoEPKvjRNS_23basisu_image_level_infoEjj
+    _ZN6basist17basisu_transcoder17start_transcodingEPKvj
+    _ZNK6basist17basisu_transcoder21transcode_image_levelEPKvjjjPvjNS_25transcoder_texture_formatEjjPNS_23basisu_transcoder_stateEj
+    createDFDUnpacked
+    createDFDPacked
+    createDFDCompressed
+    findMapping
+    interpretDFD
+    isProhibitedFormat
+    isValidFormat
+    ktxCheckHeader1_
+    ktxMemStream_construct
+    ktxMemStream_construct_ro
+    ktxMemStream_destruct
+    ktxMemStream_getdata
+    ktxTexture_calcImageSize
+    ktxTexture_calcLevelSize
+    ktxTexture1_Destroy
+    ktxTexture1_SetImageFromMemory
+    ktxTexture1_WriteToMemory
+    ktxTexture1_calcLevelOffset
+    ktxTexture1_destruct
+    ktxTexture1_glTypeSize
+    ktxTexture2_GetImageOffset
+    ktxTexture2_calcLevelOffset
+    ktxTexture2_destruct
+    vk2dfd
+    vkFormatString

lib/internalexport_write_mingw.def

@@ -0,0 +1,17 @@
+; Copyright 2019-2020 Mark Callow
+; SPDX-License-Identifier: Apache-2.0
+
+; Export internal functions used by internal test programs and the
+; validator. Using this file avoids having to decorate those internal
+; functions or updating such decorations as the tests evolve. Updating
+; this feels less obnoxious.
+
+LIBRARY libktx
+EXPORTS
+    _ZN6basisu9ResamplerD1Ev
+    _ZN6basisu9ResamplerC1EiiiiNS0_11Boundary_OpEffPKcPNS0_12Contrib_ListES5_ffff
+    _ZN6basisu9Resampler8put_lineEPKf
+    _ZN6basisu9Resampler8get_lineEv
+    _Z15swizzle_to_rgbaPhS_jyP9swizzle_e
+    appendLibId
+