figure out why linking against static MSVCRT isn't working

[andrewrk]

Here in link.cpp I had to force is_dynamic to be true to fix regressions after 5d2edac.

static void add_nt_link_args(LinkJob *lj, bool is_library) {
    CodeGen *g = lj->codegen;

    if (lj->link_in_crt) {
        bool is_dynamic = true; // g->is_dynamic;
        const char *lib_str = is_dynamic ? "" : "lib";
        const char *d_str = (g->build_mode == BuildModeDebug) ? "d" : "";

        if (!is_dynamic) {
            Buf *cmt_lib_name = buf_sprintf("libcmt%s.lib", d_str);
            lj->args.append(buf_ptr(cmt_lib_name));
        } else {
            Buf *msvcrt_lib_name = buf_sprintf("msvcrt%s.lib", d_str);
            lj->args.append(buf_ptr(msvcrt_lib_name));
        }

        Buf *vcruntime_lib_name = buf_sprintf("%svcruntime%s.lib", lib_str, d_str);
        lj->args.append(buf_ptr(vcruntime_lib_name));

        Buf *crt_lib_name = buf_sprintf("%sucrt%s.lib", lib_str, d_str);
        lj->args.append(buf_ptr(crt_lib_name));

        //Visual C++ 2015 Conformance Changes
        //https://msdn.microsoft.com/en-us/library/bb531344.aspx
        lj->args.append("legacy_stdio_definitions.lib");

        // msvcrt depends on kernel32
        lj->args.append("kernel32.lib");

We should be able to do:

-        bool is_dynamic = true; // g->is_dynamic;
+        bool is_dynamic = g->is_dynamic;

And have the full zig test suite pass on Windows.

On the other hand, this issue may become unnecessary if we get a Windows libc shipping with Zig with #514.

[Sahnvour]

I think this is an issue only when building the self-hosted compiler, right?

When applying your diff, it fails with many linker warnings and errors such as

lld: warning: LLVMAArch64CodeGen.lib(AArch64TargetMachine.obj): locally defined symbol imported: free (defined in libucrtd.lib(free.obj)) [LNK4217]

Indicating that it expects to import free from a DLL, but found it in the object files it is currently linking.

lld: warning: zig_cpp.lib(zig_llvm.cpp.obj): locally defined symbol imported: free (defined in libucrtd.lib(free.obj)) [LNK4217]

I guess it's also built with /MD[d] for the zig0 and zig1 targets, at least visual studio generated projects say so.

lld: error: undefined symbol: __imp_strdup
>>> referenced by zig_cpp.lib(zig_llvm.cpp.obj):($LN8)

__imp_XYZ are used when linking with a DLL.

By default, on windows, LLVM seems to build with /MD[d]. Could it be that, following our LLVM build instructions, a fully static build of self-hosted zig is impossible since LLVM expects dynamic CRT libraries?
It would also require rebuilding some steps of zig staticly?