Compile Windows releases with a static CRT

[alexcrichton]

This commit compiles all Rust code for the Windows release with
-Ctarget-feature=+crt-static. This is targeted at increasing the
binary compatibility of the binaries built to not rely on DLLs that
aren't always installed on Windows. Notably this statically links the C
runtime (notably used by the C++ code) and means that the final binary
relies on fewer dlls.

This in theory means that the binaries are only limited by the number of
APIs they use from Windows. Note that this also matches how we build
releases of Rust for MSVC.

[alexcrichton]

This is basically the same as #246 but for Windows, and like that I'd like to actually test the releases that get built to make sure this actually is recognized and the right place to configure this

[alexcrichton]

Ok verified working too!

Before this PR:

$ objdump -p wasmtime.exe | rg 'DLL Name'
    DLL Name: ADVAPI32.dll
    DLL Name: KERNEL32.dll
    DLL Name: ole32.dll
    DLL Name: SHELL32.dll
    DLL Name: MSVCP140.dll
    DLL Name: VCRUNTIME140.dll
    DLL Name: api-ms-win-crt-math-l1-1-0.dll
    DLL Name: api-ms-win-crt-runtime-l1-1-0.dll
    DLL Name: api-ms-win-crt-stdio-l1-1-0.dll
    DLL Name: api-ms-win-crt-string-l1-1-0.dll
    DLL Name: api-ms-win-crt-convert-l1-1-0.dll
    DLL Name: api-ms-win-crt-environment-l1-1-0.dll
    DLL Name: api-ms-win-crt-locale-l1-1-0.dll
    DLL Name: api-ms-win-crt-heap-l1-1-0.dll

After this PR:

$ objdump -p wasmtime.exe | rg 'DLL Name'
    DLL Name: ADVAPI32.dll
    DLL Name: KERNEL32.dll
    DLL Name: ole32.dll
    DLL Name: SHELL32.dll

[tschneidereit]

LGTM!