Linker error when building with strikethrough extension for Windows.

[fahrstuhl]

When building the project for Windows with mingw on Linux, the linker throws the following undefined reference error:

x86_64-w64-mingw32-gcc -o demo/bin/windows/x86_64/release/libmarkdown.so -shared godot_markdown/src/cmark.os -Ldemo/bin/windows/x86_64/release -ladvapi32 -lcmark-gfm-extensions -lcmark-gfm -lcmark-gfm-extensions
/usr/lib/gcc/x86_64-w64-mingw32/10.2.0/../../../../x86_64-w64-mingw32/bin/ld: godot_markdown/src/cmark.os:cmark.c:(.rdata$.refptr.CMARK_NODE_STRIKETHROUGH[.refptr.CMARK_NODE_STRIKETHROUGH]+0x0): undefined reference to `CMARK_NODE_STRIKETHROUGH'
collect2: error: ld returned 1 exit status
scons: *** [demo/bin/windows/x86_64/release/libmarkdown.so] Error 1

Other extension do not yet have this problem. Right now, I disabled the strikethrough extension on Windows with a compile flag.