CMake: Create liblzma.def when building liblzma.dll with MinGW-w64.

CMakeLists.txt

@@ -889,6 +889,26 @@ if(WIN32)
 
         # Export the public API symbols with __declspec(dllexport).
         target_compile_definitions(liblzma PRIVATE DLL_EXPORT)
+
+        if(NOT MSVC)
+            # Create a DEF file. The linker puts the ordinal numbers there
+            # too so the output from the linker isn't our final file.
+            target_link_options(liblzma PRIVATE
+                                "-Wl,--output-def,liblzma.def.in")
+
+            # Remove the ordinal numbers from the DEF file so that
+            # no one will create an import library that links by ordinal
+            # instead of by name. We don't maintain a DEF file so the
+            # ordinal numbers aren't stable.
+            add_custom_command(TARGET liblzma POST_BUILD
+                COMMAND "${CMAKE_COMMAND}"
+                    -DINPUT_FILE=liblzma.def.in
+                    -DOUTPUT_FILE=liblzma.def
+                    -P
+                    "${CMAKE_CURRENT_SOURCE_DIR}/cmake/remove-ordinals.cmake"
+                BYPRODUCTS "liblzma.def"
+                VERBATIM)
+        endif()
     else()
         # Disable __declspec(dllimport) when linking against static liblzma.
         target_compile_definitions(liblzma INTERFACE LZMA_API_STATIC)

cmake/remove-ordinals.cmake

@@ -0,0 +1,26 @@
+#############################################################################
+#
+# remove-ordinals.cmake
+#
+# Removes the ordinal numbers from a DEF file that has been created by
+# GNU ld or LLVM lld option --output-def (when creating a Windows DLL).
+# This should be equivalent: sed 's/ \+@ *[0-9]\+//'
+#
+# Usage:
+#
+#     cmake -DINPUT_FILE=infile.def.in \
+#           -DOUTPUT_FILE=outfile.def \
+#           -P remove-ordinals.cmake
+#
+#############################################################################
+#
+# Author: Lasse Collin
+#
+# This file has been put into the public domain.
+# You can do whatever you want with this file.
+#
+#############################################################################
+
+file(READ "${INPUT_FILE}" STR)
+string(REGEX REPLACE " +@ *[0-9]+" "" STR "${STR}")
+file(WRITE "${OUTPUT_FILE}" "${STR}")