doh: fix build for windows

[jay]

• (Windows) Define bool type for < VS2013 since those versions are
  missing stdbool.h.

• (Windows) Use size_t format specifier %Iu instead of %zu, since the
  latter is not supported by older CRTs.

• (Windows) Search and set the CA certificate bundle in the path.

Closes #xxxx

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The Makefile output looks wrong so I didn't use it to build. It did this

make CFLAGS="-I/usr/local/include" LDFLAGS="-L/usr/local/lib -lcurl"
cc -I/usr/local/include   -c -o doh.o doh.c
cc -L/usr/local/lib -lcurl  doh.o   -o doh
doh.o:doh.c:(.text+0x101c): undefined reference to `__imp__curl_easy_init'

but I'm pretty sure that's out of order and should be a link command or ordered like cc -o doh doh.o -L/usr/local/lib -lcurl

[bagder]

👍