Does not compile on Windows 10

`luarocks install cmark` yields the following error on Windows 10 (with the VS 2019 Build Tools and Windows 10 SDK):

```
C:\Program Files (x86)\LuaRocks>luarocks.bat install cmark
Installing https://luarocks.org/cmark-0.29.0-1.src.rock

cl /nologo /MD /O2 -c -Focmark_wrap.obj -IC:\Program Files (x86)\Lua\5.1\include cmark_wrap.c -I. -Iext
cmark_wrap.c
ext\cmark.h(27): error C2143: syntax error: missing ')' before '('
ext\cmark.h(27): error C2091: function returns function
ext\cmark.h(27): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(27): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(27): error C2059: syntax error: 'string'
ext\cmark.h(27): error C2059: syntax error: ')'
ext\cmark.h(111): error C2143: syntax error: missing ')' before '('
ext\cmark.h(111): error C2091: function returns function
ext\cmark.h(111): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(111): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(111): error C2059: syntax error: 'string'
ext\cmark.h(111): error C2059: syntax error: ')'
ext\cmark.h(117): error C2143: syntax error: missing ')' before '('
ext\cmark.h(117): error C2091: function returns function
ext\cmark.h(117): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(117): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(117): error C2059: syntax error: 'string'
ext\cmark.h(117): error C2059: syntax error: ')'
ext\cmark.h(122): error C2143: syntax error: missing ')' before '('
ext\cmark.h(122): error C2091: function returns function
ext\cmark.h(122): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(122): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(122): error C2059: syntax error: 'string'
ext\cmark.h(122): error C2059: syntax error: ')'
ext\cmark.h(131): error C2143: syntax error: missing ')' before '('
ext\cmark.h(131): error C2091: function returns function
ext\cmark.h(131): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(131): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(131): error C2059: syntax error: 'string'
ext\cmark.h(131): error C2059: syntax error: ')'
ext\cmark.h(136): error C2143: syntax error: missing ')' before '('
ext\cmark.h(136): error C2091: function returns function
ext\cmark.h(136): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(136): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(136): error C2059: syntax error: 'string'
ext\cmark.h(136): error C2059: syntax error: ')'
ext\cmark.h(140): error C2143: syntax error: missing ')' before '('
ext\cmark.h(140): error C2091: function returns function
ext\cmark.h(140): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(140): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(140): error C2059: syntax error: 'string'
ext\cmark.h(140): error C2059: syntax error: ')'
ext\cmark.h(144): error C2143: syntax error: missing ')' before '('
ext\cmark.h(144): error C2091: function returns function
ext\cmark.h(144): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(144): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(144): error C2059: syntax error: 'string'
ext\cmark.h(144): error C2059: syntax error: ')'
ext\cmark.h(148): error C2143: syntax error: missing ')' before '('
ext\cmark.h(148): error C2091: function returns function
ext\cmark.h(148): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(148): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(148): error C2059: syntax error: 'string'
ext\cmark.h(148): error C2059: syntax error: ')'
ext\cmark.h(207): error C2143: syntax error: missing ')' before '('
ext\cmark.h(207): error C2091: function returns function
ext\cmark.h(207): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(207): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(207): error C2059: syntax error: 'string'
ext\cmark.h(207): error C2059: syntax error: ')'
ext\cmark.h(212): error C2143: syntax error: missing ')' before '('
ext\cmark.h(212): error C2091: function returns function
ext\cmark.h(212): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(212): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(212): error C2059: syntax error: 'string'
ext\cmark.h(212): error C2059: syntax error: ')'
ext\cmark.h(218): error C2143: syntax error: missing ')' before '('
ext\cmark.h(218): error C2091: function returns function
ext\cmark.h(218): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(218): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(218): error C2059: syntax error: 'string'
ext\cmark.h(218): error C2059: syntax error: ')'
ext\cmark.h(223): error C2143: syntax error: missing ')' before '('
ext\cmark.h(223): error C2091: function returns function
ext\cmark.h(223): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(223): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(223): error C2059: syntax error: 'string'
ext\cmark.h(223): error C2059: syntax error: ')'
ext\cmark.h(228): error C2143: syntax error: missing ')' before '('
ext\cmark.h(228): error C2091: function returns function
ext\cmark.h(228): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(228): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(228): error C2059: syntax error: 'string'
ext\cmark.h(228): error C2059: syntax error: ')'
ext\cmark.h(233): error C2143: syntax error: missing ')' before '('
ext\cmark.h(233): error C2091: function returns function
ext\cmark.h(233): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(233): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(233): error C2059: syntax error: 'string'
ext\cmark.h(233): error C2059: syntax error: ')'
ext\cmark.h(240): error C2143: syntax error: missing ')' before '('
ext\cmark.h(240): error C2091: function returns function
ext\cmark.h(240): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(240): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(240): error C2059: syntax error: 'string'
ext\cmark.h(240): error C2059: syntax error: ')'
ext\cmark.h(250): error C2143: syntax error: missing ')' before '('
ext\cmark.h(250): error C2091: function returns function
ext\cmark.h(250): error C2143: syntax error: missing ')' before 'string'
ext\cmark.h(250): error C2143: syntax error: missing '{' before 'string'
ext\cmark.h(250): error C2059: syntax error: 'string'
ext\cmark.h(250): fatal error C1003: error count exceeds 100; stopping compilation

Error: Build error: Failed compiling object cmark_wrap.obj

```