cmake: workaround LTO issue on Windows.

With the GNU toolchain there's some mix-up and the "opentrack_version"
symbol isn't emitted into the object file at all. Disable LTO for the
"version" statically linked library.

The "version" statically linked library exists so that files needing the
version only need to be re-linked, not recompiled. A preprocessor global
-DVERSION=foo rebuilds the whole project after each commit. A header
definition rebuilds all include sites.

LTO in the GNU toolchain is very broken on Windows, particular the
interaction of GCC "linker plugin" injected into Binutils bfd ld. The
gold ld we can't use since it's only for ELF executables.

There's nothing alarming here at all unless there's some miscompilation
and there doesn't seem to be any. The rest of the functional changes is
changing cc -> c of that object file, and moving library definition
after the source file is already generated.

1 files changed, 11 insertions, 6 deletions

diff --git a/cmake/opentrack-version.cmake b/cmake/opentrack-version.cmake
index 9a311ff9..d753535f 100755
--- a/cmake/opentrack-version.cmake
+++ b/cmake/opentrack-version.cmake
@@ -18,14 +18,13 @@ endif()
 
 file(WRITE ${CMAKE_BINARY_DIR}/opentrack-version.h "#define OPENTRACK_VERSION \"${_build_type}${OPENTRACK_COMMIT}\"")
 
-add_library(opentrack-version STATIC ${CMAKE_BINARY_DIR}/version.cc)
-opentrack_compat(opentrack-version)
-
 set(version-string "
 #include \"opentrack-compat/export.hpp\"
 
 #ifdef __cplusplus
 extern \"C\"
+#else
+extern
 #endif
 OPENTRACK_EXPORT
 const char* opentrack_version;
@@ -34,10 +33,16 @@ const char* opentrack_version = \"${_build_type}${OPENTRACK_COMMIT}\";
 ")
 
 set(crapola-ver)
-if(EXISTS ${CMAKE_BINARY_DIR}/version.cc)
-    file(READ ${CMAKE_BINARY_DIR}/version.cc crapola-ver)
+if(EXISTS ${CMAKE_BINARY_DIR}/version.c)
+    file(READ ${CMAKE_BINARY_DIR}/version.c crapola-ver)
 endif()
 
 if(NOT (crapola-ver STREQUAL version-string))
-    file(WRITE ${CMAKE_BINARY_DIR}/version.cc "${version-string}")
+    file(WRITE ${CMAKE_BINARY_DIR}/version.c "${version-string}")
 endif()
+
+add_library(opentrack-version STATIC ${CMAKE_BINARY_DIR}/version.c)
+if(NOT MSVC)
+    SET_TARGET_PROPERTIES(opentrack-version PROPERTIES COMPILE_FLAGS "-fno-lto")
+endif()
+opentrack_compat(opentrack-version)