Building the compiler on 64-bit Windows fails in rust_builtin.c / valgrind.h (uintptr_t not defined)

[jamesluke]

As the title says. src/rt/rust_builtin.c includes src/rt/valgrind/valgrind.h, valgrind.h uses the uintptr_t type defined in <stdint.h> but does not include <stdint.h> itself.

Either rust_builtin.c needs to include <stdint.h> before valgrind.h, or valgrind.h needs to include <stdint.h> along with an include guard. I'd do this myself, but I should presumably understand the code at least slightly before I mess about with it.

[huonw]

Fixed by #16323.