Define the C++ Swift(U)Int types using the same logic as SwiftShims

The C type tha corresponds to Swift's pointer-sized `Int` and `UInt`
types varies from one platform to the next. The canonical C types are
`ptrdiff_t` and `size_t`, but we're in the depths of the compiler we
can't include the C library headers that provide them because they
introduce cyclic module dependencies. Sigh.

SwiftShims has some logic to compute these types. However, SwiftShims
is part of the Swift runtime, not the compiler, so those headers
cannot be included here. So, we clone the logic and simplify it
somewhat for our use case.

This fixes truncation issues on Windows, where the uses of
`unsigned long` and `long` for Swift(U)Int are incorrect.

Author: DougGregor

include/swift/Basic/CBasicBridging.h

@@ -21,6 +21,64 @@
 // it causes importing the "Darwin"/"Glibc" overlay module. That violates
 // layering. i.e. Darwin overlay is created by Swift compiler.
 
+// NOTE: Partially ported from SwiftShim's SwiftStdint.h. We cannot include
+// that header here because it belongs to the runtime, but we need the same
+// logic for interoperability with Swift code in the compiler itself.
+// stdint.h is provided by Clang, but it dispatches to libc's stdint.h.  As a
+// result, using stdint.h here would pull in Darwin module (which includes
+// libc). This creates a dependency cycle, so we can't use stdint.h in
+// SwiftShims.
+// On Linux, the story is different. We get the error message
+// "/usr/include/x86_64-linux-gnu/sys/types.h:146:10: error: 'stddef.h' file not
+// found"
+// This is a known Clang/Ubuntu bug.
+
+// Clang has been defining __INTxx_TYPE__ macros for a long time.
+// __UINTxx_TYPE__ are defined only since Clang 3.5.
+#if !defined(__APPLE__) && !defined(__linux__) && !defined(__OpenBSD__) && !defined(__wasi__)
+#include <stdint.h>
+typedef int64_t __swiftc_int64_t;
+typedef uint64_t __swiftc_uint64_t;
+typedef int32_t __swiftc_int32_t;
+typedef uint32_t __swiftc_uint32_t;
+typedef intptr_t __swiftc_intptr_t;
+typedef uintptr_t __swiftc_uintptr_t;
+#else
+typedef __INT64_TYPE__ __swiftc_int64_t;
+#ifdef __UINT64_TYPE__
+typedef __UINT64_TYPE__ __swiftc_uint64_t;
+#else
+typedef unsigned __INT64_TYPE__ __swiftc_uint64_t;
+#endif
+
+typedef __INT32_TYPE__ __swiftc_int32_t;
+#ifdef __UINT32_TYPE__
+typedef __UINT32_TYPE__ __swiftc_uint32_t;
+#else
+typedef unsigned __INT32_TYPE__ __swiftc_uint32_t;
+#endif
+
+#define __swiftc_join3(a,b,c) a ## b ## c
+
+#define __swiftc_intn_t(n) __swiftc_join3(__swiftc_int, n, _t)
+#define __swiftc_uintn_t(n) __swiftc_join3(__swiftc_uint, n, _t)
+
+#if defined(_MSC_VER) && !defined(__clang__)
+#if defined(_WIN32)
+typedef __swiftc_int32_t SwiftInt;
+typedef __swiftc_uint32_t SwiftUInt;
+#elif defined(_WIN64)
+typedef __swiftc_int64_t SwiftInt;
+typedef __swiftc_uint64_t SwiftUInt;
+#else
+#error unknown windows pointer width
+#endif
+#else
+typedef __swiftc_intn_t(__INTPTR_WIDTH__) SwiftInt;
+typedef __swiftc_uintn_t(__INTPTR_WIDTH__) SwiftUInt;
+#endif
+#endif
+
 SWIFT_BEGIN_NULLABILITY_ANNOTATIONS
 
 #ifdef __cplusplus
@@ -38,9 +96,6 @@ FeatureName,
 
 SWIFT_BEGIN_ASSUME_NONNULL
 
-typedef long SwiftInt;
-typedef unsigned long SwiftUInt;
-
 typedef struct BridgedData {
   const char *_Nullable baseAddress;
   SwiftUInt size;