Fixes the next issue on windows. The fontconfig library is calling
the function xmlCreatePushParserCtxt from libxml2, however, the function
declaration was being omitted because fontconfig was not defining
the LIBXML_PUSH_ENABLED preprocessor symbol. However, instead of a
compile error, C's support for implicit function declrations allows it
to happily call the function anyway, with the wrong ABI. The main issue
was the return type being implicitly declared as "int" instead of a
pointer. On my system this was causing the return pointer to be
truncated to 32 bits and then sign-extended which caused a segfault
once it was dereferenced.
I've gone ahead and added the -Werror=implicit-function-declaration
to fontconfig to avoid these issues in the future. However, this
flag didn't compile on linux so I've left it as Windows only for now.
I also needed to add the LIBXML_STATIC define because not defining it
causes some functions on windows to be declared with
`__declspec(dllimport)` which results in linker errors since we are
actually statically linking libxml2.
Makes progress getting "zig build test" to work on windows. Mostly
fixed issues around build configuration and added some branches throughout
the Zig code to return/throw errors for unimplemented parts.
I also added an initial implementation for getting the home dir.
